you need to divide 19 between 5 then you will know the growth in each month that will be 3.8
to know for example the growth in the third month you need to sum 3.8+3.8+3.8 =11.4 or do a multiplication 3.8 *3=11.4 it is the same!
here is the table complete
Month Growth
1 3.8
2 7.6
3 11.4
4 15.2
5 19
6 22.8