Solve the system of equations.

-4x+7y=20

y=3x+15

Solve by Substitution:

/ / Solve equation [2] for the variable y

[2] 5y = 15x - 4

[2] y = 3x - 4/5

/ / Plug this in for variable y in equation [1]

[1] 15x - 20• (3x-4/5) = 7

[1] - 45x = - 9

/ / Solve equation [1] for the variable x

[1] 45x = 9

[1] x = 1/5

/ / By now we know this much:

x = 1/5

y = 3x-4/5

/ / Use the x value to solve for y

y = 3 (1/5) - 4/5 = - 1/5

Solution:

{x, y} = {1/5,-1/5}