X+3y=12 and y=6x+21 system of substitution

(x, y) = (- 3, 3)

Step-by-step explanation:

given the 2 equations

- x + 3y = 12 → (1)

y = 6x + 21 → (2)

Substitute y = 6x + 21 into (1)

- x + 3(6x + 21) = 12 ← distribute

- x + 18x + 63 = 12

17x + 63 = 12 ( subtract 63 from both sides )

17x = - 51 ( divide both sides by 17 )

x = - 3

Substitute  x = - 3 into (2) for y

y = (6 × - 3 ) + 21 = - 18 + 21 = 3

solution is (- 3, 3 )