Question

I don't know how I would get this answer.

Answer 1

7-3=4
4 digits is thousands, so the highest number thats 4 digits is 9,999 so thats your answer

Answer 2

well, 10,000
same thing

Answer 3

you have to apply the product principle ( rule of product).

Answer 4

the first 3 digits are fixed, so this mean that you will combine digits from 0 to 9 on the 4 free places remained.