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),
(bt
,  -70.0), (-20.0, c
y
), (-80.0, -70.0). The overall displacement of
the four darts has the xy components (-140, -20.0). What are (a) bt
and (b) c
y
? What are the ( c) magnitude and (d) angle (relative to the
positive direction of the x axis) of the overall displacement?