The ultimate strength is MPa and the factor of safety is 3, will nearly be

Question

The diameter of  a  shaft to transmit 25kW at 1500 r.p.m., given that the ultimate strength is   MPa and the factor of safety is 3, will nearly be                                         

         (a) 12 mm                            (b) 6 mm

         (c) 20 mm                            (d) 26 mm