Управляющая компания ответила сразу.

Because the subject is компания, and компания is a feminine noun.

In the Russian past tense, verbs agree with the subject in gender and number:

• он ответил = he answered
• она ответила = she answered
• оно ответило = it answered
• они ответили = they answered

So:

• Управляющая компания ответила = the management company answered

Even though управляющая компания is a two-word phrase, the main noun is компания, so the verb takes the feminine form.

It is in the nominative case, because it is the subject of the sentence.

Both words match each other:

• управляющая — nominative, feminine, singular
• компания — nominative, feminine, singular

Russian adjectives normally agree with the noun they describe in case, gender, and number, so управляющая changes to match компания.

Grammatically, it comes from the verb управлять and is historically a participle, but in this kind of phrase learners can usually treat it like an adjective.

So управляющая компания works like:

• management company
• literally something like managing company

In modern everyday Russian, this is a very standard set phrase, especially in housing/building contexts.

This is a question of aspect.

• ответила is perfective
• отвечала is imperfective

Here, ответила is used because the sentence talks about one completed reply: the company replied, and that action is finished.

Сразу also strongly favors the perfective verb here, because it means immediately / right away, so the idea is that the reply happened promptly as a completed event.

Compare:

• Компания ответила сразу = The company replied right away.
• Компания отвечала = The company was answering / used to answer / answered repeatedly, depending on context.

Here сразу means immediately, right away, or at once.

It is an adverb, so it modifies the verb ответила.

So:

• ответила сразу = replied immediately

Depending on context, English might translate it as:

• right away
• straight away
• immediately
• at once

Yes. Russian word order is more flexible than English word order.

This sentence could also be:

• Управляющая компания сразу ответила
• Сразу ответила управляющая компания

All of these are possible, but the emphasis changes a little.

A rough guide:

• Управляющая компания ответила сразу = neutral, with a little extra emphasis on сразу
• Управляющая компания сразу ответила = also very natural, often slightly more straightforward
• Сразу ответила управляющая компания = stronger emphasis on immediately

So the original sentence is normal, but it is not the only possible order.

Russian does not have articles like English the and a/an.

So компания can mean:

• a company
• the company

The exact meaning depends on context.

That means Управляющая компания ответила сразу could be understood as:

• The management company replied right away or
• A management company replied right away

In real life, context usually makes it clear which one is meant.

The stress pattern is:

управля́ющая компа́ния отве́тила сра́зу

A rough pronunciation guide:

• управля́ющая = oo-prav-LYAI-yu-shcha-ya
• компа́ния = kam-PA-nee-ya
• отве́тила = at-VYE-tee-la
• сра́зу = SRA-zoo

For learners, the most important thing is to remember the stressed syllables, because Russian vowel sounds often change when they are unstressed.