Gym Membership Fee Calculation

A fitness center uses a specific formula to determine the membership fee for its clients. The monthly membership fee is calculated using the formula:

$F = 15 + 0.5x$, where $F$ is the total fee in dollars and $x$ is the number of gym classes attended per month. Calculate the membership fee when a client attends 20 classes in a month. Round your answer to two decimal places as needed.