A body weighing 13 kg is suspended by two strings 5 m and 12 m long, their other ends being fastened to the extremities of a rod 13 m long. If the rod be so held that the strings are inclined at 60 degrees to the vertical, what is the tension in the shorter string?

a) 54 N
b) 65 N
c) 78 N
d) 91 N