A golfer hit a golf ball with a force of 15 N and the ball traveled with an acceleration of 25 m/s/s. What

is the mass of the golf ball?

If he didn't hit it exactly horizontally OR in outer space, then the question can't be answered, because gravity would influence its acceleration.

If he DID hit it exactly horizontally, and its acceleration at the immediate instant after the hit was 25 m/s², then, from Newton's 2nd law of motion:

F = m·A

m = F / A

m = (15 N) / (25 m/s²)

m = 0.6 kg (the mass of about 13 actual real regulation golf balls)