Answer:
The area he can cover with that weapon is 1,256 miles².
Step-by-step explanation:
Assuming that the Jedi won't move and that he can shoot in every direction, he'd be shooting at a circle with a radius of 20 miles. Therefore the are that he can cover with that weapon is the area of the circle, which is shown below:
area = pi*r²
area = 3.14*(20)²
area = 3.14*400
area = 1,256 miles²
The area he can cover with that weapon is 1,256 miles².