Let number of of newspaper ads be x. \ \

Let number of of radio ads be y.

Total number of ads = 50. \ \

So the equation is .

    -> (1) \ \

The cost of newspaper ads = $600. \ \

The cost of radio ads = $300.

Total cost = $24,000.

So, the equation is .

         (Divide each side by 100) \ \

             (Divide each side by 3)

      (Substitute equation y=50-x)

              (Subtract: )

              (Subtract 50 to each side)

                      (Subtract: )

\ \

               (Substitute )

                       (Subtract: )

The newspaper ads = 30. \ \

The radio ads = 20.