Consider that the sum of the interior angles of a triangle is equal to 180°. Then, by using the given measure in the image, you have:
18u + 18u + 108 = 180 simplify like terms left side
36u + 108 = 180 subtract 108 both sides
36u = 180 - 108
36u = 72 divide by 36 both sides
u = 72/36
u = 2
Hence, the value of u is 2
