An icicle drips at a rate that can be represented by the function f(x) = −x2 + 9x − 18, where 0 ≤ x ≤ 10 and x is the number of hours after the sun has risen. When f(x) is a negative number, the icicle is not dripping. Determine the values when the icicle starts and stops dripping.

x = −3 and x = 6
x = 3 and x = −6
x = 3 and x = 6
x = −3 and x = −6