Chapter 4, Problem 100P

An iceboat sails across the surface of a frozen lake with constant acceleration produced by the wind. At a certain instant the boat’s velocity is $\text{(6}\text{.30 <mover accent="true"> i <mo> ^ </mo> </mover> }-\text{ 8}\text{.42 <mover accent="true"> j <mo> ^ </mo> </mover> )}$ m/s. Three seconds later, because of a wind shift, the boat is instantaneously at rest. What is its average acceleration for this 3.00 s interval?