Two functions, function a and function b, are shown below:

function a

x y
7 14
8 16
9 18
which statement best compares the rate of change of the two functions?
the rate of change of both functions is 2.
the rate of change of both functions is 3.
the rate of change of function a is greater than the rate of change of function b.
the rate of change of function b is greater than the rate of change of function a.