Solve for x please help me

It's C.

Step-by-step explanation:

12x+4+9x+8=180

Combine like terms 21x+12=180

Subtract 12 from both sides 21x=168

Divide each side by 21 21x/21=168/21

x=8

by definition, an arc subtended by a central angle of some given measure has the same measure. so .

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