well, we have a missing point of R, but since is part of one of the tangent lines, we can safely assume is the point where the PR of 5 inches is at.
what is the angle at point R? namely the ∡SRP, well, SR is a tangent, RP is a radius line, they both touch/intersect at point R, thus R is the point of tangency for those two, and the point of tangency is always a 90° angle.
