Find the ordered pair (x,y) that satisfies the system of equations
x + y = 15
x - y = 3 - 4x + 7y
x + y = 15 → y = 15 - x (1)
x - y = 3 - 4x + 7y → 5x -8y = 3 (2)
Sub (1) into (2) for y
5x - 8 ( 15 - x) = 3
5x - 120 + 8x = 3
13x = 123
x = 123 / 13
y = 15 - x = 15 - 123 / 13 = (195 - 123) /13 = 72 / 13