Answer: 30 degrees
Work Shown
The two arc measures add to 180 degrees
(arc LM) + (arc MN) = 180
(13x-10) + (7x-10) = 180
20x-20 = 180
20x = 180+20
20x = 200
x = 200/20
x = 10
Then,
arc MN = 7x-10
arc MN = 7*10-10
arc MN = 60 degrees
Use the inscribed angle theorem to divide that amount in half to get,
angle NLM = (1/2)*(arc MN)
angle NLM = (1/2)*(60)
angle NLM = 30 degrees