In 2000, the population was 6.08 billion and growing at the rate of 1.21 % each year

In 2000, the population was 6.08 billion and growing at the rate of 1.21 % each year

a)write the function of represent the popluation of the world ?
b)when will the population reach 7 billion?
c)what will be the population in 2020?