So to solve for a variable, we must isolate such variable onto 1 side of the equation. In this case, we must isolate the x variable. Firstly, subtract both sides by Fy:
[tex]Dx=M-Fy[/tex]
Next, divide both sides by D:
[tex]x=\frac{M-Fy}{D}[/tex]
Your final answer is [tex]x=\frac{M-Fy}{D}[/tex]