The fastest way to review a solution is to click on a particular step, as that allows you to review the logic which was applied.  There are some sections of a simplification where switching to 'a lot of steps' can be helpful (click on the 'Options' tab to configure for more solution steps). 

That particular solution is an addition of fractions, so it begins with a common least denominator.  Then the numerator must be simplified by factoring it.  A common portion of factoring a quadratic expression is to divide the middle term into two portions (32x is expressed as '12x + 20x') in order to obtain common factors.  '3x' is common to '3x^2 + 12x' and '20' is common to '20x + 80'.