w = 2p /T = 5 rad/s

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

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