At t=0, population is given by 100.

As population increases by 50% every 3 years,

After 3 years population will be given by 100 + (50/100)*100

                                                              = 100(1+50/100)3/3

After 6 years population will be given by 100 + (50/100)*100 + (50/100)*(100 + (50/100)*100)

                                                             = 100(1+50/100)6/3

Similarly population after 9 years will be given by 100(1+50/100)9/3

Arguing analogously population after t years will be given by 100(1+50/100)t/3

For the second part, put t=22. So the answer is given by 100(1+50/100)22/3 = 1955.85

But the population cannot be in fractions so the population is 1955. Ans.