What is the solution to this system of equations?
x − 2y = 15
2x + 4y = -18

a. x = 1, y = -6

b. x = 1, y = -7

c. x = 3, y = -6

e. x = 3, y = -7

Use the property of substitution to solve:
2 ( x - 2y = 15) ... 2x - 4y = 30
                           2x + 4y = -18

subtract     4x = 12  
divide by 4        x =3   place into original equation 3 - 2y = 15
                                                                                   -2y = 12
                                                                                     y = -6
(3, -6)