Can you help me on the backsolving question 7 on pg. 37? Its got me stumped even with the backsolving.

Sure! I trust you already looked at the solution in the back, which walks through the backsolve, so maybe I’ll show you the algebra?

Let’s say is the number of subway trips and is the number of car trips. She commutes 5 days, so she takes 10 total trips: . We also know she spends a total of $74.75, so our second equation is . Solve the system!