Step 1:
We assume that A, q, and, b, are real numbers (where y could be a variable).
Step 2:
Terms with z to the left of the equation. Independent terms of z to the right of the equation.
Az - yz = qb
Step 3:
Common factor z.
z (A - y) = qb
Step 4:
Clear z.
z = qb / (A - y)
Answer:
z = qb / (A - y)