b)
\frac{x+3}{x+4} + \frac{x-4}{x-1}=\frac{(x+3)(x-1)+(x-4)(x+4)}{(x+4)(x-1)}=\frac{x^2-x+3x-3+x^2-16}{x^2-x+4x-4}=\frac{2x^2+2x-19}{x^2+3x-4}
c)
\frac{x+6}{x^2-9} + \frac{x-2}{x+3}=\frac{x+6}{(x-3)(x+3)}+\frac{(x-2)(x-3)}{(x+3)(x-3)}=
\frac{x+6+x^2-3x-2x+6}{(x+3)(x-3)}=\frac{x^2-4x+12}{x^2-9}