I assume, that the number 120 is 100% - because it's the output value of the task.
If 120 is 100%, so we can write it down as 120=100%.
We know, that x is 25% of the output value, so we can write it down as x=25%.
Now we have two equations:
1) 120=100%
2) x=25%
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:
120/x=100%/25%
Solution for what is 25% of 120:
120/x=100/25
(120/x)*x=(100/25)*x - we multiply both sides of the equation by x
120=4*x - we divide both sides of the equation by (4) to get x
120/4=x
30=x
x=30
The answer is: 25% of 120=30
