Question 943732
Simple fraction skills from elementary school.


Assuming you have this:
{{{-(7x-8y)/(4x)+(x+2y)/(6x)+3}}}
the lowest common denominator is 12x.  Bring all rational expressions to higher terms to use denominator 12x.


{{{(-(7x-8y)/(4x))(3/3)+((x+2y)/(6x))(2/2)+3(12x)/(12x)}}}


{{{(-(7x-8y)(3)+(x+2y)*2+36x)/(12x)}}}


Continue working with the numerator, and... then simplify if possible.