As a rule, I encourage users to begin a solution with 'a few steps' and only increase the number of steps when the additional information is helpful rather than overwhelming/confusing... for this particular simplification, however, using the 'Options' tab to select 'a lot of steps' is actually helpful to determine exactly why '(x-31)' appeared as a factor! 

Two key common factors are "(x+5)^2" and "(x-7)" - notice that both of those terms are common in the initial numerator. 

Notice that factoring out "(x+5)^2(x-7)" leaves being 'a mess' that is nice simplified down to (x-3).