(a) Let \(t=\angle APQ\). The common chord bisects PQ, so \[\cos t=\frac{5r/6}{r}=\frac56,\qquad t=\cos^{-1}(5/6)\approx0.585686.\] Each boundary arc subtends \(2t\), hence \[P=2(r\cdot2t)=4rt\approx2.34r.\]

(b) The lens comprises two equal segments. Each segment is a sector of angle \(2t\) less the triangle between its two radii: \[A=2\left[\frac12r^2(2t)-\frac12r^2\sin(2t)\right]=r^2[2t-\sin(2t)]\approx0.250r^2.\]