Why did we use ustedes instead of usted ?

Question

¡________ vamos a regalar un coche!We are buying you a car!(HINT: Choose the right word for "you" ("ustedes"))Why did we use ustedes instead of usted ?

Answer

Hola Omer,
Since the answer is nosotros vamos... (we are going to...), the "you" in the question has to be plural: ustedes. If you ask the question with usted, the answer would have to be yo voy...

Answer

I still didnt understand, i just wanted to understand why the answer is "les" instead of "le" ? Because the word "you" is not plural formal in this example.

Answer

Hola Omer
That "les" is referring to a plural "you" (ustedes, not usted), so:

Nosotros les vamos a regalar  un coche.
We are going to give you (plural) a car.

If it was only one person receiving that car, then we should say:

Nosotros le vamos a regalar  un coche. 
We are going to give you (singular -formal) a car.

I hope this clarified it.
Saludos
Inma

Answer

Omer that is such a good question!