If a and b are the two numbers, 3a+2b=120.
There are many solutions. For example, b=0, a=40; b=3, a=38; b=6, a=36; b=9, a=34, etc.
There are also fractional solutions, for example: b=1, a=118/3, etc.
You need two equations if you have two unknowns if you want unique values of a and b.