this is the problem i have i dont understand

Did you mean to finish the question as "what is the number" instead of "what is the difference"?

You need to think about how the words translate into symbols

difference means (-) subtraction

four times means (4x) multiplying something by 4

a number (n) n can represent anything for the time being

the same means (=) equals

two times means (2x) multiplying something by 2

Then you put the sentence into symbols and numbers

4 x n - 3 = 2 x 7

4n - 3 = 14

4n = 17

n = 17/4 = 4.25