Hey there! I'm happy to help!
First let's find the radius. The radius is half of the diameter.
9/2=4.5
Here's how to find the volume of any sphere.
You cube the radius.
4.5³=91.125
You multiply by 3.14
91.125(3.14)=286.1325
And finally we multiply by 4/3.
286.1325(4/3)=381.51
We round to the nearest tenth, giving us a volume of 381.5 in^3.
Have a wonderful day! :D