Problem 8
A prime number is where it has factors of 1 and itself, and no other factors.
Example: 7 is prime because 1 and 7 are the only factors.
If we take two whole numbers from the set {2,3,4,5,6,...} and multiply them together, then we'll get some composite number. Eg: 2*3 = 6 is composite.
We know it's composite because those two values we multiplied are factors of the number, and those two values we picked aren't 1 and the prime number itself.
==========================================
Problem 9
p = some prime number
p+p = adding the prime to itself = 2p
2p = some even number
2 is a factor of 2p, which means 2p is not prime. The expression 2p represents a composite number. Regardless of whatever prime you pick for p.
Example: p = 11 gives
p+p = 11+11 = 22
or
2p = 2*11 = 22
The value 22 is not prime since we have factors 2 and 11.