First, find any two factors of 20. For example, 4 and 5. Then, you look at two factors of each number. You should be able to see that 4 simplifies to 2*2 and both of those numbers are primes (the only factors are 1 and itself). 5 is already a prime and so you have the prime factors. Therefore, the number 20 can be expressed as:
2^2 x 5
Now have a go at the other parts of the question :)
Let me explain the process to you,
First, find any two factors of 20. For example, 4 and 5. Then, you look at two factors of each number. You should be able to see that 4 simplifies to 2*2 and both of those numbers are primes (the only factors are 1 and itself). 5 is already a prime and so you have the prime factors. Therefore, the number 20 can be expressed as:
2^2 x 5
Now have a go at the other parts of the question :)