In English there are several different question-words or phrases that you use when asking a “number question”. Two of them are “what” and “how many”. So you can say, for example “What is your phone number?” and “How many students are there in this class?”
In Indonesian, when you ask a question that demands a number as its answer you use just one question-word: berapa.
Tanggal berapa Anda lahir?
What’s you birth date?
Berapa nomor telepon Anda?
What’s your telephone number?
Berapa harganya?
How much it is?
Jam berapa?
What time is it?
Berapa jam?
How many hours?
Berapa lama Anda pergi?
How long did you go?
