Is 80 a rational number

Bob the builder is making 480kg of cement mix. this is made by cement, sand and gravel in the ratio 1: 3: 4

Need solving this 2nd limit problem.

15. jiovanni is looking in to two different companies that offer study guides for math exams. test prep 101 charges a $5 flat fee and an additional $0.25 per problem. math charges a $2 flat fee and an additional $0.50 per problem. how many prablems would make the costs of the two companies be equal? varibles: equations/eniqualities{ {