Answer: z = A/C - Mx/C
Explanation:
Try to get rid of anything that is not z.
So subtract Mx on both sides, this cancels out +Mx on the left side and on the right A is subtracted by Mx.
Cz = A - Mx
Then, divide C on both sides to cancel the C on the right. Then you get:
z = A/C - Mx/C