Question 304796
{{{(-90s^2+55st+35t^2)/(-5s+5t)}}}
:
Factor, then cancel out the 5
{{{5(-18s^2+11st+7t^2)/5(-s+t)}}} = {{{(-18s^2+11st+7t^2)/(-s+t)}}}
:
Factor out -1 to change the signs
{{{(-1)(18s^2-11st-7t^2)/-1(s-t)}}} = {{{(18s^2-11st-7t^2)/(s-t)}}}
: 
Factor the numerator, cancel the (s-t)'s
{{{((18s+7t)(s-t))/(s-t)}}} = (18s + 7t)