Quantes espelmes necessitem? En necessitem sis per al pastís.

Because quantes means how many and it agrees with the noun it refers to.

Here the noun is espelmes (candles), which is feminine plural, so Catalan uses:

• quants for masculine plural
• quantes for feminine plural

So:

• Quantes espelmes...? = How many candles...?

This agreement is something English does not do with how many, but Catalan does.

Necessitem is the 1st person plural present indicative of necessitar (to need).

So it means:

• necessitem = we need

A few related forms are:

• necessito = I need
• necessites = you need
• necessita = he/she/it needs
• necessitem = we need
• necessiteu = you all need
• necessiten = they need

In both sentences, the subject is we, even though Catalan does not need to state nosaltres.

Catalan often leaves out subject pronouns when the verb ending already makes the subject clear.

So instead of saying:

• Nosaltres necessitem...

Catalan very naturally says:

• Necessitem...

Because -em in necessitem already tells you it means we.

This is very common in Catalan, just as in Spanish or Italian.

Here en is a pronoun that replaces espelmes.

So the second sentence literally works like:

• En necessitem sis = We need six of them

It avoids repeating espelmes.

You can think of it as referring back to an unspecified quantity of something already mentioned:

• Quantes espelmes necessitem?
• En necessitem sis.

That is basically:

• How many candles do we need?
• We need six (of them).

This en is very common in Catalan when talking about quantities.

Because en is an unstressed object pronoun, and in normal affirmative sentences in Catalan, these pronouns usually go before the conjugated verb.

So:

• En necessitem sis

not:

• Necessitem en sis

This is standard pronoun placement in Catalan.

Very roughly:

• en
  • verb + quantity

Examples:

• En vull dos = I want two of them
• En tenim moltes = We have many of them
• En necessitem sis = We need six of them

Yes, absolutely.

That would be a fully natural sentence meaning:

• We need six candles for the cake

The version with en is used because espelmes was already mentioned in the question, so Catalan prefers not to repeat the noun unnecessarily.

So both are correct:

• Necessitem sis espelmes per al pastís
• En necessitem sis per al pastís

The second one sounds more connected to the previous question.

You can answer with just Sis in conversation, especially if the context is obvious.

But En necessitem sis is a fuller, more complete answer. It sounds natural and clear, and it shows the normal Catalan structure for answering a quantity question.

So these are all possible, with slightly different levels of completeness:

• Sis. = Six.
• Sis espelmes. = Six candles.
• En necessitem sis. = We need six of them.

The sentence you were given is useful because it teaches the grammar pattern, not just the shortest possible reply.

Per al means for the.

It is made from:

• per a = for
• el = the

So:

• per a + el = per al

That gives:

• per al pastís = for the cake

This is a very common combination in Catalan.

Because per al comes from per a + el, while pel comes from per + el.

In standard Catalan, many learners are taught:

• per al = for the
• pel = by the / through the / along the / because of the, depending on context

So in this sentence, the idea is purpose:

• six candles for the cake

That is why per al pastís is the expected form.

You may sometimes hear variation in informal speech or depending on dialect, but for learners, per al pastís is the safest standard choice here.

Espelma means candle. Its plural is espelmes.

It is feminine, so:

• singular: una espelma
• plural: unes espelmes

That feminine gender is why the question uses:

• quantes espelmes

not:

• quants espelmes

In Catalan, adjectives, articles, and words like quants/quantes often agree in gender and number with the noun.

Because sis is the number six, and in this use it does not change for gender.

So you say:

• sis espelmes = six candles
• sis llibres = six books

Unlike one or two hundred, some numbers may vary in certain languages, but sis stays the same here.

Pastís means cake.

In per al pastís, it tells you the purpose of the candles:

• the six candles are for the cake

So the structure is:

• En necessitem sis = We need six of them
• per al pastís = for the cake

Together:

• En necessitem sis per al pastís = We need six of them for the cake

Yes. Catalan uses the normal closing question mark:

• Quantes espelmes necessitem?

Unlike Spanish, Catalan does not use an opening inverted question mark (¿).

So the punctuation here is very similar to English.