Step-by-step explanation:
your teacher makes a mistake : "complementary" means the angles sum up to 180 degrees. not 90 degrees.
but it is clear what he/she means here.
AOC + BOC = 90
AOC = BOC + 30
we substitute the second equation into the first :
BOC + 30 + BOC = 90
2×BOC = 60
BOC = 30 degrees
AOC = BOC + 30 = 30 + 30 = 60 degrees
so,
1.
AOC + BOC = 90
2.
BOC + BOC + 30 = 90
3.
BOC = 30
4.
AOC = 60
