Write a formula that will jenny determine how much she will earn in one week
a=total amount earned
h=hours worked in one week
b=number of memberships sold in one week

It's the same thing as before, A = BH
Remember A will always be some kind of Total, in this sense. Then you have to figure out what is the constant factor, that will be H then figure out what makes the constant factor vary. In this case it's the number of memberships since that can vary from week to week but her hours can not.
Like how you can vary the number of cans but you can not vary the price that they sell the cans.