Equations have right sides, and then they have left sides. Soooooo, generally when we "solve" equations, we isolate the variable. In this case, the variable would be x. So, your task is to move everything to one side of the equation except x.
The MVT says that there will be at least one place in an interval [a,b] where the slope of the tangent line to the graph will have the same slope as the secant line through [a,f(a)] and [b,f(b)]. You have found the slope of the secant line. So, you're not done.
Start pressing the button!