Respuesta :

Hello from MrBillDoesMath

Answer:   12

Discussion

Let the number of aerobic classes be "n".

Then

"membership"        "aerobic" class

12  + 3n                 =  4n

Subtract 3n from each side:


12 + (3n - 3n) = 4n - 3n =n =>

12 = n


Thank you,

Mr. B