$\displaystyle T(n) = T\left(3n\over4\right) + T\left(n\over6\right) + 5n$ is not in the proper form for the Master theorem so I can't really apply it. The only idea I had was changing the $\displaystyle T\left(n\over6\right)$ to $\displaystyle T\left(3n\over4\right)$ and then we would have $\displaystyle T(n) = 2T\left(3n\over4\right) + 5n$ for the MT to apply.
I would thereby bound the function by another function. Probably not a good solution and possibly wrong. Is there a better way to solve this?