A man bought 42 stamps, some 13¢ and some 18¢. How many of each kind did he buy if the cost was $6.66? If x represents the number of 13 cent stamps and y the 18 cent stamps, which system represents the problem? x + y = 42 and 0.13x + 0.18y = 6.66 x + y = 6.66 and 0.13x = 0.18y 0.13x + 0.18y = 42 and x + y = 6.66