Can someone tell me how I ought the answer this question:

'Suppose that an epidemic in a community of 50,000 starts with 80 people infected, and that 15 days later, 640 are infected. How many are infected 25 days into the epidemic?'

The correct answer is supposd to be 2483, and the question should be based on the logistic growth model.

Please help, as I have no idea what to do!!