Find the answer .its both questions

Yes because when you want to find the prime factors of the number that you are multiplying, you need to multiply the numbers first.

21. It is not necessary to use a calculator as you already know 4 numbers which can be multiplied to make 17017 ( the final number). As those 4 numbers are all prime numbers the PFD would be 17017 = 7 x 11 x 13 x 17

22. Following the pattern, and additional 0 increases the incidies by 1, therefore, as 1 billion has 9 '0s', the PFD would be 1,000,000,000 = 5^9 x 2^9