What methods are useful to create the equation of a line?

What is the average rate of change for this function for the interval from x=2 to x=4 ?

The linear combination method is applied to a system of equations as shown. 4(.25x + .5y = 3.75) → x + 2y = 15 (4x – 8y = 12) → x – 2y = 3 2x = 18 what is the solution of the system of equations? (1,2) (3,9) (5,5) (9,3)

Adam used 1072.4 gallons of water over the course of 7 days. how much water did adam use, on average, each day?