A pencil costs $p$ dollars and an eraser costs $e$ dollars. Mark buys $3$ more pencils than erasers, and he buys $7$ pencils. Write an expression that represents the amount of money that Mark spent, in dollars.

Step-by-step explanation:

Mark buys 7 pencils, and a pencil costs p dollars, so the total cost of all of the pencils is 7p dollars. He buys 3 more pencils than erasers, so he buys 4 erasers. Each eraser costs e dollars, so the total cost of all the erasers is 4e dollars. Thus, Mark spent dollars in total.

Hope this helped! :)