Can someone please with all the answers

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?

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

Three students, javier, sam, and corrine, participated in a fundraiser where people donated a certain amount of money per lap that the student ran. each student also had some initial donations that were collected before the run. the equations that represent each student's total donation, y, based on the number of laps ran, x, is shown below. match each equation with the correct rate of change for that student.