bus passes cost $1.50 each
15 passes plus discount card cost $29.50
the cost of the discount card
Use the given relation bewteen the costs.
... 15×$1.50 + (discount card) = $29.50 . . . given
... $22.50 + (discount card) = $29.50 . . . . simplify
... (discount card) = $7.00 . . . . . . . . . . . . . . subtract $22.50
Paul spent $7 on the discount card.