31. ** Predict/Calculate The point charges in FIGURE 19−42 have the following values: q1 = +2.1 μC, q2 = +6.3 μC, q3 = −0.89 μC. (a) Given that the distance din Figure 19−42 is 4.35 cm, find the direction and magnitude of the net electrostatic force exerted on the point charge q1. (b) How would your answers to part (a) change if the distance d were doubled? Explain. FIGURE 19-42 Problems 31, 32, 46, and 55