What is the simplified form of (x+5)/(3x+4) + (x+4)/(x+3)

A. (2x+9)/(4x+7)

B. (4x^2+24x+31)/(3x^2+13x+12)

C. (4x^2+24x+31)/(4x+7)

D. (2x+9)/(3x^2+13x+12)