Answer:
s+18=120
s=102
Explanation:
Basically, she had 120 after everything was done, so we know 120 is on the right side of the equal sign. We know she had an unknown number of songs and after she added 18 it was 120. That means the equation is s+18=120
Now to solve it is simple, just isolate s by subtracting 18 on both sides.
s+18=120
-18 -18
s=102