Hello. To answer this questions, we need to remember some properties about fractions and equivalences.
Starting by the question 9:
Call the population 5 years ago by P. If the population has decreased 12000 in these 5 years and this represents a decrease of 3%, so it means the new population is 0.97P.
With this, we can make the following equation:
P - 12000 = 0.97P
Subtract 0.97P and sum 12000 in both sides of the equation
0.03P = 12000
Divide both sides of the equation by a factor of 0.03
P = 3600000