empty set? solution set? many solutions?

5x - y  =  54    --->     5x  -   y  =   54

3y  =  5x - 72   --->   -5x + 3y  =  -72

Add down:                          2y  =  -18

Divide by 2:                          y  =  -9

Substitue this back into either equation to get the value for x.

There will be one, and only one, solution.