#(df) / dx = 3 cdot (frac{3x + 4}{6x + 7})^2 cdot d/dx u/v#
#u = 3x + 4 Rightarrow u' = 3#
#v = 6x + 7 Rightarrow v' = 6#
#(df) / dx = 3 cdot (frac{3x + 4}{6x + 7})^2 cdot (3 (6x + 7) - (3x + 4) 6)/(6x + 7)^2#
#(df) / dx = 3 cdot (frac{3x + 4}{6x + 7})^2 cdot (-3)/(6x + 7)^2#