Well
4 x 5 = 20
and
5 x 5 = 25
I'm sure a calculator could help you out with this, But if you don't have access to a calculator I'll show you how to multiply. It's just like adding, Let's use 6 x 7 for example. Take the first number ( Which is 6 in this case ) and look at the second number ( Which would be 7 ) The second number represents how many times you would add the first number together. So:
6 + 6 + 6 + 6 + 6 + 6 + 6 = 42 ( We add 6 together 7 times )
So
6 x 7 = 42
There are faster methods but this is probably the best way to start out.