Can someone answer 22 step by step?

In the final round of trivia competition, contestants were asked to name as many states that begin with the letter m as they could in 15 seconds. the bar graph shows the number of states the contestants were able to name. how many contestants participated in the final round of the competition?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Use the elimination method to solve the systems of equations.choose the correct ordered pair. 7x+4y=39