A 20-cm radius ball is uniformly charged to 80 nC. (a) What is the ball’s charge density (C/m3)? (b) How much charge is enclosed by spheres at points 5, 10 and 20 cm from the center? (c) What is the electric ﬁeld strength at points 5, 10 and 20 cm from the center? ATTEMPT: part a: i don't know how to get the answer, but i know A=4(pi)r^2 and i know how to convert the nC to C. but my units of A will be m^2 and i need m^3. part b: i think the charge at 5, and 10 is zero because all of the charge is on the outside of the ball. so to find the charge at 20cm (surface) i think it would be 100% of the charge so 80nC. part c: since there's no charge at 5 or 10 cm i think E=0. at 20cm i would use the formula E=kq/r^2. am i on the right track?