Two aluminum alloy plates each 10 mm thick and 1 m long are welded without crowning by multipass tungsten inert gas butt welding. The joint configuration is V-type with 600 angle and root gap is maintained at 5 mm. if electrode of 5 mm diameter with 500 mm length is used for welding, then the number of electrodes required is (a) 7 (b) 9 (c) 11 (d) 13