Find the rate of change of the function h(x) = 2 x on the interval 2 ≤ x ≤ 4

For a linear function, the instantaneous rate of change is everywhere equal to the slope. Thus the rate of change of the function h(x)=2x on the interval 2≤x≤4
The rate of change of the function given will equal to its slope, thus;
slope,m=(y-1-y)/(x_1-x)
=(2*4-2*2)/(4-2)
=(8-4)/2
=4/2
=2

the answer is 2