If I divide a certain number by 7, the answer is the same as if I subtracted 3 from it. What is the number?

Question

 I don't understand how to solve this question and have already tried trial and error but with no resut

Answer 1

n/7=n-3

n=7(n-3)

n=7n-21

-6n=-21

6n=21

n=3.5 is the number

check: 3.5/7=1/2 and 3.5-3=0.5=1/2