Jamil pays $10.00 for a swim club membership and $1.50 for each day that he goes to the pool. The equation is c=1.5d+10. What is the dependent variable?

The dependent variable depends on the value of the independent variable

normally it is something like

dependent variable=something times independent variable+something

it is normally the result or what the equation is

therefor the dependent variable is c (how much he has to pay total)

A dependent variable is something that depends on other factors. In you problem the value of "c" depends on the amount of days Jamil goes swimming therefore c is the dependent variable and d is the independent variable