1. Recurrence relation

a. Note that 1800/1200 = 1.5.

b. Next, take 1.5* 1800 =2700, and that is the next population.

c. Now 1.5*2700 = 4050.

2. To calculate the number of bats at the 12^th count, take 1200 * 1.5¹¹ = 1200 *86.5 = 103,797