smc

We can make two equations (assume angle D is y): $y+2x=180$ and $4y+x=180$. We find that $x=\frac{540}{7}$. Now we have to convert this to radians. 360 degrees is $2\pi$ radians, so since we have $\frac{540}{7}$ degrees, the answer is $\frac{3\pi }{7}$ which is $\boxed{\frac{3\pi }{7}}.$