The country's population in 1994 was 98 million. in 2001 it was 103 million estimate the population in 2018.round to the nearest million

Populations generally increase as an exponential function.  In a short period of time, it could be approximated as linear (first degree).  Depending what your teacher expects, 

Linear model:
rate of increase = (y2-y1)/(x2-x1)=(103-98)/(2001-1994)=5/7 million per year.
From 2001 to 2018, there are 17 years.  So add 17(5/7) millions to population of 2001.

exponential model:
Over 7 years, the ratio of populations is 103/98, so the annual ratio is (103/98)^(1/7)=1.007134, about 0.7134%.
Use the compound interest formula to find the population growing at the same rate from 2001 for 17 years:
population at 2018 = 103 millions * 1.007134^17 which is a little over 116 millions.

I’m not sure what it is i sorry : ((