Using the formula:
a = (Vf - Vi) / t
Our initial velocity is 0 m/s, and our final velocity is 8.15 m/s, with a time period of 5 seconds:
a = (8.15 - 0.0) / 5
a = 1.63 m/s^2
If you know the acceleration due to gravity on the Moon, you can confirm this answer. The recorded gravitational acceleration on the Moon is 1.62 m/s^2.