In this exercise we have to use the knowledge of trapezoid to calculate the value of the angle, so we have:
[tex]ONP=80[/tex]
So we know that the angle LMN is a supplementary interior angle, like this:
[tex]m < LMN = 180-50 = 130[/tex]
And the angle LMN and MNP form an isosceles trapezoid so:
[tex]m< LMN = m
For me, the angle MNO forms an opposite parallelogram, in this way
[tex]m< MNO = 50[/tex]
Putting all this information together we find that;
[tex]m < ONP = m MNP - m
See more about trapezoid at brainly.com/question/11600014