Combine as indicated by the signs. write answer in descending powers of x.
(x+6/x^2+8x+15) + (3x/x+5) - (x-3/x+3)

now one denominator is x^2 + 8x + 15 if we factorise then (x +3)(x +5) now in expressions which have like x+3 as denominator ...you multiply and divide them by x+5 and once u get denominator equal you can add numerator easily