What is the measure of ∠nlm?
m∠nlm =

Angle L and Angle M are congruent base angles.
Angle N is half of the apex angle. (Look closely and you can see the arrows).
2(6x + 1) + 2(4x - 11) = 180
Distribute the 2's
12x + 2 + 8x - 22 = 180
Combine like terms
20x - 20 = 180
Add 20 to both sides
20x = 200
Divide both sides by 20
x = 10
Plug 10 into the base angle expression.
4x - 11;
4(10) - 11 = 40 - 11 = 29
Angle NLM = 29 degrees