The correct option is (d) 60Nm

To elaborate: We know, N1/N2 = T1/T2

N1 = speed of pinion

N2 = speed of gear wheel

T1 = number of teeth of gear

T2 = number of teeth of pinion

1200/N2 = 120/40

N2 = 400 r.p.m.

Since power transmitted by both gear will be equal

T1ω12 x ω2

torque transmitted by gear, = 60 N-m.