Question

9 less than the product of a number q and 5 is r

Answer 1

9 - 5q = r

Since there are two unknown variable namely q and r. We can't solve any of the unknown by providing a number. Instead we can provide the formula on how to look for its corresponding value.

We know that:
r = 9 - 5q

9 - 5q = r
-5q = r - 9
-5q / -5 = (r - 9) / - 5
q = (r - 9) / -5