There are two forces on the 1.49 kg box in the overhead view of the figure but only one is shown. For F1 = 16.8 N, a = 10.5 m/s2, and θ = 23.1∘, find the second force (a) in unit-vector notation and as (b) a magnitude and (c) a direction. (State the direction as a negative angle measured from the +x direction.)