Isuck at graphs asap question below

What is the value of x in the following equation. -x ^3/2 = -27

If p(a) = 0.70 and p(b) = 0.20, then a and b are independent events if

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! )