Answer:
The period of revolution is 5.2 years.
Step-by-step explanation:
The period of revolution about the Sun for an asteroid can be found using Kepler's third law:
(1)
Where:
p: is the period =?
a: is the semimajor axis (average distance from Sun) = 3 AU
By entering "a" value into equation (1) we have:

Therefore, the period of revolution about the Sun for an asteroid in the middle of the asteroid belt is 5.2 years.
I hope it helps you!