It's a little tough to know what to say, since you posted in this generic category. Had you posted in Algebra, there would be a good answer. Had you posted in Differential Equations, there would be simpler answer. The nature of the question rather leans toward the differential equation formulation:
The Initial Growth Rate is r = 0.15
The Carying Capacity is K = 100 (in millions)
You have only to substitute your given population values and calculate the actual growth at that level. Calculating the Growth Rate is a matter of dividing by the population again. At P = 80, I get 3%.