Q is a right angle and AB = 4√2, so the two legs AQ = BQ = 4.
P and R are the midpoints → they're the centers of the arcs, radius = 2.
The shaded "almond" is bounded by 2 arcs. Because of the 90° at Q, each arc is a quarter-circle:
each = ¼ × 2π(2) = π
Two arcs → π π = 2π