Sorry about the unit :D. For part (c), is that the value of charge Q found in part (a) equal to the surface charge density multiply by the surface area which is 4pi*r^2? If that is right I get rho(s)=11,789 nC/m^2
I think it must be 20 because when taking partial derivative of D(theta component)*sin(theta) respect to theta we can obtain derivative of sin(theta)^2=2sin(theta)cos(theta). This is the first time I post thread so excuse me about the math formulas