(b) For displacement $OQ = 40$ cm; let $t_{1}$ be the time taken then
$40 = 41\sin\frac{2\pi}{24}t_{1},$ on solving $t_{1} = 5.16$ s
For displacement $OQ = - 9$ cm, let $t_{2}$ be the time taken then $9 = 41\sin\frac{2\pi}{12}t_{2}$,
On solving $t_{2} = 0.84$ s
Total time $= 5.16 + 0.84 = 6.00$ s