(this sign < means angle)
the triangle PQS is an isoscele triangle (both legs are radii of the circle).
Therefore <SPQ = <SQP.
Using the theorem of the sum of angles in a triangle you get:
<QSR = 2 * 24° = 48°
Therefore the arc is:
arc(QR) = 48° * (2pi)/360° * (1/2)PR = (4/15)pi * (1/2)PR ≈ 0.8377... * PR