8.) Indicate whether the graphs of the following will have a maximum or a minimum:

a.) f(x) = x^2 - 9

b.) f(x) = 8x - 3x^2

c.) f(x) = -(3 - x)^2

9.) If y varies directly with x, and y = 10 when x = 15, find y when x = 6.

10.) If x varies inversely as y and x = 2 when y = 8, find x when y = 17.

11.) If y varies directly as x and inversely as z^2, and y = 3 when x = 2 and z = 4, what is the value of x when y - 6 and z = 2?