QUIZ 16
12, 13,  14, 15, 23, 24, 25, 26, 27, 28, 37, 38 , 41, 42 
12    - 1.5x10^2 N,  5.6x10^2 N and  -4.2x10^2 N, on the charges from  left to right; positive direction: rightward.
14      6.19x10^7 N, along diagonal, away from center.
24      2.34x10^5 N/C,  south
26      7.42x10^5 N/C,  up
28      8.4x10^7 N/C, toward negative charge.
38      A:  4.5x10^6 N/C, up   B:    1.2x10^7 N/C, 56 degrees above  positive x-axis.
42      (a) right  (b) magnitude =  6.4x10^2 N C  (c)