Let's say x is longest side, y is shortest side and z is the other side. So we have some equations such that
\(x+y+z=57\) (by the first sentence)
\(x=(y+z) -3\) (by the second sentence)
\(2y=x-15\) (by the third sentence)
By the second equation, we have \(y+z=x+3\) and if we use it in the first equation, then \(x+y+z=x+(x+3)=57\). So \(x=27\)
Since \(x=27\), if we use it in the third equation the we have \(2y=x-15=27-15=12\) then \(y=6\)
Therefore \(z=24\)
