Over which interval is the graph of f(x) = –x2 + 3x + 8 increasing?

Over which interval is the graph of f(x) = –x2 + 3x + 8 increasing?

a. (–∞, 1.5)
b. (–∞, 10.25)
c. (1.5, ∞)
d. (10.25, ∞)