The figure below shows two right angled triangles ΔOAB and ΔOQP with right angles at vertex A and P, respectively, having the common vertex O. The lengths of some of the sides are indicated in the figure: OA = 3, AB = 1, OP = 2, PQ = 1. (Note that the figure is not drawn to scale.) AB and OP are parallel. What is ∠QOB? [Figure: see page 16 of source PDF]