You are solving the two equations for x.
9.
r = 4 + 7x - sx
We need to solve for x. x is only found in the right side. First, just flip the sides to find x only in the left side.
4 + 7x - sx = r
We want all terms with x on the left side, and all terms without x on the right side. Now we subtract 4 from both sides.
7x - sx = r - 4
Factor x in left side.
x(7 - s) = r - 4
Divide both sides by 7 - s.
12.
3z + 8 = 12 + 3x - z
Since x is only in the right side, flip the sides.
12 + 3x - z = 3z + 8
We need to isolate x in the left side, so subtract 12 from both sides and add z to both sides.
3x = 3z + 8 - 12 + z
3x = 4z - 4
Divide both sides by 3.
