1. Factor both expressions
x^2 + x - 12 = (x + 4) (x - 3)
x^2 + 2x - 15 = (x + 5) (x - 3)
The LCM is just all the different factors we have listed....so....
(x - 4) (x + 5) ( x - 3) ⇒ second answer
2. Notice that we can see if the first numerator factors using the second denominator
(w + 6) ( w - 4) 8
____________ + _____
(w + 6) ( w - 5) ( w - 5)
( w - 4) + 8
______ _____
(w - 5 ) (w - 5)
( w - 4 + 8)
_________
( w - 5)
w + 4
_____
w - 5