solve the linear system from problem 1 using elimination
4x-y=5
4x+4y=-4
subtract the two equations to ELIMINATE the x-term
-5y = 9 __ y = -9/5
substitute back to find x
4x + 9/5 = 5
4x-y=5
4x+4y=-4
-5y = 9 __ y = -9/5
substitute back to find x
4x + 9/5 = 5