First find probability of getting a serve in that's not an ace. To make things concrete, take 30 serves. Then 24 go in (8 out of 10), and 2 are aces (1 in 15). That means 22 of 30 serves go in, but are not aces, i.e., probability = 11/15.

The probability you want is 4C3 * prob of 3 aces * prob of in but not ace =

4 * (1/15)^3 * (11/15) = 0.000869