What is the answer to this equation?

In the diagram of circle o, what is the measure of zabc?

In which direction does the left side of the graph of this function point? a(x) = 3x - x2 + 4x - 2

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! )