21. Tony Ring wants to attend Northeast College. He will need \( \$ 25,000 \) in \( 4 \) years from today. Assume Tony's bank pays \( 11 \% \) interest compounded semiannually. What must Tony deposit today so he will have \( \$ 25,000 \) in \( 4 \) years?
Joe earns \( \$ 9 \) per hour. He worked \( x \) hours on both Wednesday and Friday, and \( 8 \) hours on both Tuesday and Saturday. Write an expression to represent how much Joe earned.