Answer:
see explanation
Step-by-step explanation:
Given ∠ DOC = 90° then
∠ DOB = 90 - p and
Since AOB is a straight angle , then
4p + 90 - p = 180
3p + 90 = 180 ( subtract 90 from both sides )
3p = 90 ( divide both sides by 3 )
p = 30
4p = 4 × 30 = 120
Then
∠ DOB = 180° - 4p = 180° - 120° = 60°
