Ray MO bisects ML and MN, meaning that the two parts are parallel to each other. This means you can set the two equal to one another. 3x-20 = x+10
2x+30 = 15
X=15
You are then able to plug 15 in for the variable of X.
Ray ML
3(15)-20
45-20
= 25°
Ray MN
(15) + 10
= 25°
Or you could assume they are the same measurement as they are equal.