What is the rate change for each consecutive pair of X's?

Question

Using the table shown, what is the rate of change for each consecutive pair of x's? Please put your answers in y/x format, unless the denominator is 1 - then you should enter the whole number.

X values: 1,2,3,4
Y Values: 15,20,25,30

Answer 1

dy/dx = 5/1 = 5

Answer 2

If you are looking for delta y / delta x then

first pair delta y = 5, delta x = 1: dy/dx = 5
2nd pair delta y = 5 delta x = 1: dy/dx = 5
3rd pair delta y = 5 delta x = 1: dy/dx = 5

The data describe a line given by y = 5x + 10

The question doesn't seem to make much sense.