A hollow shaft (d0 = di, where d0 and di are the outer and inner diameters respectively) needs to transmit kW power at rpm. If the maximum permissible shear stress is MPa, d0 is:
a) d0 = (16kW / πn)²
b) d0 = (32kW / πn)²
c) d0 = (64kW / πn)²
d) d0 = (128kW / πn)²
