هذا السؤال صعب جدا، ولذلك أحتاج إلى مساعدة.

Because السؤال is a masculine singular noun in Arabic, and the demonstrative must match it in gender and number.

• هذا = this for masculine singular nouns
• هذه = this for feminine singular nouns

So:

• هذا السؤال = this question
• but هذه المشكلة = this problem, because المشكلة is feminine

In Modern Standard Arabic, the normal way to say this question is:

هذا السؤال

So unlike English, Arabic often uses both the demonstrative and the definite article together.

A useful contrast is:

• هذا السؤال = this question
• هذا سؤال = usually this is a question

So the الـ on السؤال is important here.

Because صعب here is not an adjective directly attached to the noun; it is the predicate of the sentence.

Arabic is saying:

• هذا السؤال صعب = This question is difficult

Here, صعب functions like is difficult, so it is normally indefinite.

Compare:

• السؤال الصعب = the difficult question
  Here الصعب is a regular adjective describing the noun.

• السؤال صعب = the question is difficult
  Here صعب is the predicate.

That is why it does not take الـ.

In Arabic, the present-tense verb to be is usually not written or spoken in sentences like this.

So Arabic says:

• هذا السؤال صعب
  literally something like this question difficult

but it means:

• This question is difficult

This kind of sentence is called a nominal sentence in Arabic.

If you wanted the past tense, Arabic would use a verb such as كان:

• كان هذا السؤال صعبًا = This question was difficult

Because جدا normally comes after the adjective or adverb it intensifies.

So Arabic says:

• صعب جدا = very difficult

not the equivalent of very difficult with very first, as in English.

This is a very common Arabic pattern:

• مهم جدا = very important
• سريع جدا = very fast
• جميل جدا = very beautiful

In fully vocalized Arabic, it is written جِدًّا.

ولذلك is made of three parts:

• و = and
• لِ = for / because of
• ذلك = that

So literally it is something like and for that, but in natural English it means:

• and therefore
• and so
• for that reason

In this sentence, it links the two ideas:

• the question is very difficult
• therefore, I need help

You can also use لذلك by itself without و if the sentence structure allows it.

أحتاج is the first-person singular imperfect form of the verb احتاج.

That means it means:

• I need
• or, depending on context, I am needing

The prefix أـ at the beginning often marks I in the imperfect tense:

• أكتب = I write
• أفهم = I understand
• أحتاج = I need

In this sentence, the natural translation is simply I need.

Because the verb احتاج normally takes the preposition إلى in Modern Standard Arabic.

So Arabic says:

• أحتاج إلى مساعدة = I need help

A good way to think about it is that احتاج إلى behaves a bit like to be in need of.

This is one of those cases where Arabic and English structure things differently:

• English: need help
• Arabic: need to/toward help structurally, with إلى

So إلى is required by the verb.

Because the speaker means help in a general, nonspecific sense.

• أحتاج إلى مساعدة = I need help / some help
• أحتاج إلى المساعدة = I need the help / the assistance

The indefinite form is the natural choice when you are asking for help generally, not referring to some specific help already known to both speaker and listener.

The final ة is called taa marbuuTa.

Usually, when you pause on the word, it sounds like -a:

• مساعدة ≈ musaaʿada

But when grammar endings are fully pronounced, the t sound appears:

• after إلى, it would be مساعدةٍ in full case pronunciation
• this is pronounced roughly musaaʿadatin

So learners often hear it as -a in normal speech, but grammatically it can behave like a t.

A fully vocalized version is:

هَذَا السُّؤَالُ صَعْبٌ جِدًّا، وَلِذَلِكَ أَحْتَاجُ إِلَى مُسَاعَدَةٍ.

A few useful notes:

• السؤالُ has ـُ because it is in the nominative
• صعبٌ also has ـٌ because it is the predicate and is nominative
• جِدًّا is an adverbial expression
• مساعدةٍ has ـٍ because it comes after the preposition إلى, so it is genitive

In normal Arabic writing, these short vowels and case endings are usually omitted, so you most often see:

هذا السؤال صعب جدا، ولذلك أحتاج إلى مساعدة.