If you look along the downward sloping line you can see that:
85+2x+x-10=180 combine like terms on left side
3x+75=180 subtract 75 from both sides
3x=105 divide both sides by 3
x=35
Now if L and M are parallel, angle 3 must be equal to x-10 because they are vertical angles (equal opposing angles). We know now that x=35 so:
angle 3 =35-10=25°
