We want to solve for the amount of money he pays each month. This is represented by y in the equation. This means we want to isolate y in the equation:
x = t - yz
We first want to subtract t from each side:
x - t = t - yz - t
x - t = -yz
Now we want to cancel the negative sign and z. We can isolate both of these at the same time; divide both sides by -z: