Let's check it by substituting m=2 into the original and your answer to see
if they are the same:

125+m^3          (m+5)(m^2-5m+25)
125+2^3          (2+5)(2^2-5·2+25) 
125+8            (7)(4-10+25)   
133              (7)(19)
                 133

Substituting a number such as 2 is usually a good check.  You can pick
m=3 also if you want to be doubly sure

125+m^3          (m+5)(m^2-5m+25)
125+3^3          (3+5)(3^2-5·3+25) 
125+27           (8)(9-15+25)   
152              (8)(19)
                 152
We are doubly sure it is correct.

Edwin