Ax + 3b = 2f
Solve for x.

The answer is x=(2/a)f - (3/a)b. 

Explanation:
We want to isolate x, which means we must cancel everything else on that side of the equals sign. We start with the term farthest from x, which is 3b. Since it was added, we cancel it by subtracting. This gives us ax=2f-3b.
 
Next we have an a to cancel. Since it is beside x, it has been multiplied; this means we cancel it by dividing. Dividing both sides by a, we have x=(2f-3b)/a. We can rewrite this as each term of the answer being divided by a, or x=(2/a)f - (3/a)b.