Which is the largest interval over which the function shown in the table is decreasing?

Which expression is equivalent to sq-80

This stem-and-leaf plot represents the heights of the students on ralph's basketball team. one student's height is missing from the plot. if the mean height of all the students on the team is 61 inches, what is the missing height? a. 55 in. b. 59 in. c. 61 in. d. 65 in.

Math i have no idea how to do a and b