لم أجد رقم الغرفة في الرسالة، لذلك ذهبت إلى الشركة مبكرا.

Because لم is the standard way to negate a past action in MSA when it is followed by the imperfect verb.

• لم أجد = I did not find
• لا أجد usually means I do not find or I am not finding

So in this sentence, the speaker is talking about something completed in the past, which is why لم is the right choice.

After لم, Arabic uses the imperfect form of the verb, but the whole phrase has a past negative meaning.

So:

• أجد by itself can mean I find / I am finding
• لم أجد means I did not find

Grammatically, لم makes the imperfect verb jussive. In a fully vocalized form, it would be أجدْ with a final sukūn.

This is a very common Arabic pattern:

• أكتب = I write
• لم أكتبْ = I did not write

The dictionary form is وَجَدَ = to find.

Arabic verbs change form depending on person:

• وَجَدَ = he found
• أَجِدُ = I find
• لَمْ أَجِدْ = I did not find

The initial و of the root does not appear in this particular imperfect form. This is normal for some verbs whose root begins with و.

So even though أجد and وجد look a bit different, they are forms of the same verb.

This is an iḍāfa construction, often translated as X of Y.

• رقم = number
• الغرفة = the room

Literally, رقم الغرفة is number of the room, but natural English says the room number.

In Arabic, iḍāfa is very common for noun combinations like:

• باب البيت = the door of the house = the house door
• اسم الطالب = the name of the student = the student’s name

So رقم الغرفة is the normal Arabic way to say room number.

In an iḍāfa construction, the first noun usually does not take الـ.

So Arabic says:

• رقم الغرفة not
• الرقم الغرفة

The definiteness of the whole phrase comes from the second noun. Since الغرفة is definite, the whole phrase رقم الغرفة becomes definite too.

This is a key rule of iḍāfa:

• first noun: no الـ
• second noun: can be definite or indefinite
• the whole phrase gets its definiteness from the second noun

في means in.

So:

• في الرسالة = in the message/letter

After a preposition such as في, إلى, من, على, the noun that follows is in the genitive case.

In fully vocalized Arabic, that would be:

• في الرِّسالةِ

In normal writing, the case ending is usually not written, so you just see في الرسالة.

Because ر and ش are sun letters.

The article is written as الـ, but before a sun letter, the ل sound is not pronounced. Instead, the following consonant is doubled.

So:

• الرسالة is pronounced ar-risālah
• الشركة is pronounced ash-sharikah

It is still written with الـ in both cases. This is a pronunciation rule, not a spelling change.

لذلك means therefore, for that reason, or so.

In this sentence, it connects the two ideas:

• I did not find the room number in the message
• therefore, I went to the company early

Yes, لذلك is fairly standard and somewhat formal, which fits MSA well.

A simpler alternative would be using فـ:

• لم أجد رقم الغرفة في الرسالة، فذهبتُ إلى الشركة مبكرًا.

That also means I didn’t find the room number in the message, so I went to the company early.

The ت marks first person singular in the past tense.

• ذهبَ = he went
• ذهبتُ = I went
• ذهبتَ = you went, masculine
• ذهبتِ = you went, feminine

In normal unvoweled writing, ذهبت could represent several of these, but in this sentence the meaning makes it clear that it is ذهبتُ = I went.

Because ذهب usually takes إلى to express movement to a place.

• ذهبتُ إلى الشركة = I went to the company

This is similar to English go to.

Without إلى, the sentence would sound incomplete or would need a different structure.

Here مبكرًا means early, and it functions like an adverb in English.

It comes from the adjective مبكر = early, but in this sentence it is used in the accusative adverbial sense:

• ذهبتُ إلى الشركة مبكرًا = I went to the company early

So although the word itself is adjective-based, its job here is adverbial: it tells how/when the action happened.

In fully vocalized writing, it would normally appear as مبكرًا with tanwīn fatḥ.

Yes. Arabic word order is flexible.

You can say:

• لم أجد رقم الغرفة...
• أنا لم أجد رقم الغرفة...

Both are correct. The version without أنا is more neutral and natural, because the verb already tells you the subject is I.

Starting with the verb is very common in Arabic, especially in MSA. Adding أنا can give extra emphasis, like I myself didn’t find it.

A fully vocalized version would be:

لَمْ أَجِدْ رَقْمَ الغُرْفَةِ فِي الرِّسَالَةِ، لِذٰلِكَ ذَهَبْتُ إِلَى الشَّرِكَةِ مُبَكِّرًا.

This shows several useful things:

• لَمْ gives a past negative meaning
• أَجِدْ is jussive after لم
• رَقْمَ is the direct object, so it is accusative
• الغُرْفَةِ is genitive because it is the second noun in an iḍāfa
• الرِّسَالَةِ is genitive after في
• ذَهَبْتُ shows first person singular past
• مُبَكِّرًا is in the accusative adverbial form

In normal Arabic writing, most of these endings are omitted, but they are still understood grammatically.