Question 1042489
The wording of this problem is somewhat ambiguous.  The population increased by 4 times the previous year's population.  To me, that means the first year was 17, and the 2nd year was 68+17=85.  That is 17*5^1
The third year would be 85*4=425, and that is the increase, added to the start of 85.  That is 17*5^2=17*25=425.
The 9th year would be 17*5^8=6,640,625
For the population to be 4 times what it was the previous year, a different picture, it would be 17*4^8=1114112