Find the gain or loss per cent when :
(i) C.P =Rs. 620 and S.P =Rs. 713
(ii) C.P =Rs. 675 and S.P =Rs. 630
(iii) C.P =Rs. 345 and S.P =Rs. 372.60
(iv) C.P =Rs. 80 and S.P =Rs. 76.80