The product of X and 7 equals 28

When you are looking for this, the best way to do this is to divide 28 by 7. This will give you 4.
The other way to do this is to list the factors of 28, which are 1,2,4,7,14,28, and you will then be able to see which two are paired.
In this case, x is 4.
Hope I have been able to help you

510 i looked it up so i know this is right because 15% of 3400 is 510