In a parallelogram, opposite angles are congruent.
This means that the four angles of the parallelogram are:
![L = x+40,\quad M = 3x,\quad N = x+40,\quad O = 3x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/am2x1j5zxo7t7i1eyifpz7bbtvyvjqvefn.png)
Moreover, the sum of the interior angles of a polygon with n sides is 180(n-2). So, the sum of the interior angles of a parallelogram is 360.
This means
![L+M+N+O = 360 \iff 2(x+40)+2(3x) = 2x+80+6x = 360 \iff 8x = 280 \iff x = 35](https://img.qammunity.org/2020/formulas/mathematics/middle-school/gwumwd7jdpt2rsdgssppvfalpw86knqq2y.png)
And since
, we have
![O=3\cdot 35=105](https://img.qammunity.org/2020/formulas/mathematics/middle-school/cduzz37adcw1gzsq2dp3d1rg2a30195izf.png)