Pick to solve the system of equations using the (elimination, substitution) method, i would (multiply equation 1 by -1 and add the equations together, multiply equation 2 by -3 and add the equation together, replace x in equation 1 with -x+15, replace y in equation 1 with -x+15, or multiply equation 2 by -1 and add the equations together) in order to solve for y.