in the figure shown, which pair of angles must be complementary?

∠aoc and ∠dob

∠cod and ∠dob

∠cob and ∠aoc

∠aoc and ∠cod

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )