How do I solve these three problems?

instructure.com/courses/3/4/5/3 14. Solve the system by elimination (addition) (other "non-guessing" methods will bring you 3 points less): (7 pts) 78 - 11y = 12 ( 58 - 7y = 18 15.Tickets for a concert were sold to adults for $3 and to students for $2. If the total receipts were $824 and the number of adult tickets was twice as many as that of student tickets, then how many of each were sold? (Hint: set up two equations in two variables and solve the system obtained; no variables in your answer: guesses will not bring you any points.) You may wish to fill out the table below. (8 pts) Total cost, $ Adult tickets Student tickets Amount of tickets Price of a ticket, $ I 3 2 What's true: y=2x? x=2 y? Choose correct version! Total: 824 16.At Mr. Russa's garage sale, all books were one price, and all magazines were another price. Robert bought four books and three magazines for $1.45, and Jennifer bought two books and five magazines for $1.25. What was the price of a book and what was the price of a magazine? (Hint: set up two equations in two variables and solve the system obtained; no variables in your answer; do not mix dollars and cents in your answer: guesses will not bring you any points.) (7 pts) instructure.com/courses/3/4/5/3 14. Solve the system by elimination (addition) (other "non-guessing" methods will bring you 3 points less): (7 pts) 78 - 11y = 12 ( 58 - 7y = 18 15.Tickets for a concert were sold to adults for $3 and to students for $2. If the total receipts were $824 and the number of adult tickets was twice as many as that of student tickets, then how many of each were sold? (Hint: set up two equations in two variables and solve the system obtained; no variables in your answer: guesses will not bring you any points.) You may wish to fill out the table below. (8 pts) Total cost, $ Adult tickets Student tickets Amount of tickets Price of a ticket, $ I 3 2 What's true: y=2x? x=2 y? Choose correct version! Total: 824 16.At Mr. Russa's garage sale, all books were one price, and all magazines were another price. Robert bought four books and three magazines for $1.45, and Jennifer bought two books and five magazines for $1.25. What was the price of a book and what was the price of a magazine? (Hint: set up two equations in two variables and solve the system obtained; no variables in your answer; do not mix dollars and cents in your answer: guesses will not bring you any points.) (7 pts)