The rate of change uses the same formula as slope
We can pick any two consecutive points
Let t= 1000
Using the formula y = 187.44121
Let t = 1500
Using the formula y = 721.72633
We can find the rate of change
rate of change = ( y2-y1) / ( x2-x1)
= ( 721.72633 - 187.44121)/ ( 1500-1000)
={534.28512}/{500}
=1.06857024 millions of people per year