Partial answers to some of the even questions:

ch. 21
4. Total charge is 6.83*10^5 C
50. Magnitude is 132 N/C
56. (a) magnitude is 1.14*10^5 N/C
62. (a) charges are +, -, +, top to bottom.


ch. 22
6. S1: zero. S2: +24 Nm^2/C
30. (a) magnitude 2.82*10^5 N/C. (c) magnitude 1.69*10^5 N/C
48. (a) -3Q/(28*pi*R^3)