Problem 4 (10 points) Three particles with charges q1 = +10 MC, q2 = -20 MC, and q3 = +25 MC are positioned at the vertices of an isosceles triangle as shown in the figure. Let a = 12 cm and b = 6.0 cm. 93 a a 92 91 (a) How much work must an external agent do to exchange the positions of q, and q3? (b) (b) How much work must an external agent do to exchange the positions of q, and q2, instead