Halliday, Resnick & Walker — Vectors: Problem 21

An ant, crazed by the Sun on a hot Texas afternoon, darts over an xy plane scratched in the dirt. The x and y components of four consecutive darts are the following, all in centimeters: (30.0, 40.0), (bx, -70.0), (-20.0, cy), (-80.0, -70.0). The overall displacement of the four darts has the xy components (-140, -20.0). What are (a) component bx and (b) component cy? What are (c) magnitude and (d) angle (relative to the positive direction of the x axis) of the overall displacement?