Pick One... 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.