the angle for a straight line is 180°. since the question gave you 100°, this means the other angle to complete the straight line is 80°. you know, 100°- 80°. then, the type of angle is corresponding angle. meaning ; the 80° angle is the same as (x+10)°. hence, to find the value of x, form an equation.
Solution:
(x + 10)° = 80°
x = 80° - 10°
x = 70°