You mean their sum is 12?
A) x + y = 12
B) x -y = 4 then we add both equations:
2x = 16
x = 8
y = 4
Solve for z:
5 (z + 6) - 2 = 9 z
5 (z + 6) = 5 z + 30:
5 z + 30 - 2 = 9 z
Add like terms. 30 - 2 = 28:
5 z + 28 = 9 z
Subtract 9 z from both sides:
(5 z - 9 z) + 28 = 9 z - 9 z
5 z - 9 z = -4 z:
-4 z + 28 = 9 z - 9 z
9 z - 9 z = 0:
28 - 4 z = 0
Subtract 28 from both sides:
(28 - 28) - 4 z = -28
28 - 28 = 0:
-4 z = -28
Divide both sides of -4 z = -28 by -4:
(-4 z)/(-4) = (-28)/(-4)
(-4)/(-4) = 1:
z = (-28)/(-4)
The gcd of 28 and -4 is 4, so (-28)/(-4) = (-(4×7))/(4 (-1)) = 4/4×(-7)/(-1) = (-7)/(-1):
z = (-7)/(-1)
(-7)/(-1) = (-1)/(-1)×7 = 7:
Answer: z = 7
