Find the sum of 12a + 7b, −6a − 9, and 14a − 12b.

a) 20a - 5b - 9
b) 20a + 5b - 9
c) 20a - 5b + 9
d) 20a + 5b + 9

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step-by-step explanation:

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x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18