two angle that form a linear pair are supplementary meaning they add to equal 180° (straight line).
make the bigger angle = x
then smaller angle = x - 30°
x + x - 30 = 180
2x - 30 = 180
2x = 180 + 30
2x = 210
x = 210/2
x = 105
The question is to find the smaller angle which was: x - 30
105 - 30 = 75°