1.build the fraction x+5/x+3 to an equivalent fraction whoes denominator is x^2-x-12
2. add and simplify: x/x+2 +4x-3/x^2-4
since x^2-x-12 = (x-4)(x+3), just multiply top and bottom by (x-4)
x/(x+2) + (4x-3) / (x+2)(x-2)
requires a common denominator of (x+2)(x-2). So, just multiply the first term top and bottom by (x-2) and then just add the numerators.