Question 250563
I assume you are to simplify the following:
{{{(3/(x^2-13x-68)) - (2/(x^2-20x+51))}}}
We need to factor both denominators first. we get
{{{(3/((x-17)(x+4))) - (2/((x-3)(x-17)))}}}
The common denominator is:
(x-17)(x+4)(x-3). 
We change the numerators to
{{{(3*(x-3)/((x-17)(x+4))) - (2*(x+4)/((x-3)(x-17)))}}}
distribute and combine like terms in the numerator to get:
{{{(x-17)/((x-17)(x+4)(x-3))}}}
cancel the x-17 to get
{{{1/((x+4)(x-3))}}}