Solve the following math problem step by step. The last line of your response should be of the form Answer: \boxed{$Answer} where $Answer is the answer to the problem.

<image>RSTV is a trapezoid with bases $\overline{R V}$ and $\overline{S T}$ and median $\overline{M N}$. Find $x$ if $M N=60, S T=4 x-1,$ and $R V=6 x+11$