A man generates a symmetrical pulse in a string by moving his hand up and down. At t=0 , the point in his hand moves downwards from mean position. The pulse travels with speed 3 m/s on the string and his hand passes 6 times in each second from the mean position. Then, the point on the string at a distance 3 m will reach its upper extreme first time at t=
a. 1.25 s
b. 1 s
c. 11/12 s
d. 2423 s