Aman 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?

Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)