Jack and Jill are maneuvering a 3400 kg boat near a dock. Initially the boat's position is < 2,0,3 > m and its speed is 1.1 m/s. As the boat moves to position < 4,0,2 > m, Jack exerts a force of <-420, 0, 210 > N, and Jill exerts a force of < 160, 0, 320 > N.

Which person exerted a force perpendicular to the displacement of the boat?
a) Neither Jack nor Jill.
b) Both Jack and Jill.
c) Jill
d) Jack.