Volume would normally be given as inches^3....I'm going to assume that it is supposed to be
215 in ^3
The paint can is a cylinder.....and the volume of a cylinder is
pi * radius ^2 * height
Filling in what we know, we have
215 = pi * radius^2 * 7.5
Divide both sides by pi * 7.5
[215 / ( pi * 7.5) ] = radius^2
Take the square root of both sides
sqrt [ 215 / (pi * 7.5) ] = radius = about 3.02 inches = about 3 inches to the nearest whole number
Hope that helped....!!!