Algebra

First off, let's combine some like terms and move all terms to one side. 

We get $6x^{2}-21x-31=0$. Unfortunately, this can't be factored without radicals, so let's use the Qudratic Formula. 

We get $x=\frac{21\pm \sqrt{(-21)^{2}-4\cdot 6(-31)}}{2\cdot 6}$. Simplifying, we get 

$x=\frac{\sqrt{1185}+21}{12}\\ x=\frac{-\sqrt{1185}+21}{12}$

We want to take the biggest value of x we could, which would be $x=\frac{\sqrt{1185}+21}{12}$. 

Thanks! :)