we are given the value of y.....y = -2x + 21...so we are going to sub in -2x + 21 in for y in the other equation.
-4x + 6y = -18
-4x + 6(-2x + 21) = -18....now we distribute through the parenthesis.
-4x - 12x + 126 = -18... simplify
-16x + 126 = -18.....subtract 126 from both sides
-16x + 126 - 126 = -18 - 126....simplify
-16x = -144...now divide both sides by -16
(-16/-16)x = -144/-16...simplify
x = 9
now we can use either equation...sub in 9 for x and solve for y
y = -2x + 21
y = -2(9) + 21
y = -18 + 21
y = 3
now we can check our answers...
-4x + 6y = -18
-4(9) + 6(3) = -18
-36 + 18 = -18
-18 = -18 (correct)
so ur solution is : (9,3)
