2. We assume, that x is the value we are looking for. 3. If 39 is 100%, so we can write it down as 39=100%. 4. We know, that x is 15% of the output value, so we can write it down as x=15%. 5. Now we have two simple equations: 1) 39=100% 2) x=15% where left sides of both of them have the same units, and both right sides have the same units, so we can do something like that: 39/x=100%/15% 6. Now we just have to solve the simple equation, and we will get the solution we are looking for.
7. Solution for what is 15% of 39
39/x=100/15 (39/x)*x=(100/15)*x - we multiply both sides of the equation by x 39=6.66666666667*x - we divide both sides of the equation by (6.66666666667) to get x 39/6.66666666667=x 5.85=x x=5.85 now we have: 15% of 39=5.85