You can
put this solution on YOUR website! .
One way to solve it is to reduce to the quadratic equation
x*(x+7) = 638.
The rest is just arithmetic, and I sincerely hope you can complete it on your own.
Another way is to take the square root of 638:
= 25.26 and then to check numbers in vicinity of 25.
By doing in this way, I found 22 and 29 in 10 seconds 22*29 = 638.