T = 2p /5 s
at t = T/8, y = 4 cos(5X2p /5X8)sin 6x = 4 cos(p /4)sin6x = 2.8 sin6x
Also k = 2p /l = 6 rad/m
l = 2p /6 = p /3 m
At this instant (t = T/8), y = 0 (ie a node) if sin 6x = 0 or x = 0 (and every (1/2)l from there).
At x = +p /12, y = 2.8sin6p /12 = 2.8 sin(p /2) = 2.8
Answer is B