A closed – coiled helical spring is made of 5mm diameter wire coiled to 50 mm mean diameter. Maximum shear stress in the spring under the action of an axial force is 20 N/mm2. The maximum shear stress in a spring made of 3mm diameter wire coiled to 30 mm mean diameter under the action of the same force will be nearly
(a) 20 N/mm2 (b) 33.3 N/mm2
(c)55.6 N/mm2 (d) 92.6 N/mm2