Answer:
In mathematical statements, it can be expressed as y = kx. This reads as “y varies directly as x” or “y is directly proportional as x” where k is constant in the equation. Example: y is directly proportional to x, when x = 15, y = 30.
4x-8 = 31
4x = 31 + 8
4x = 39
x = 9.75

so about 53 kids didn't have costumes.