[SOLVED] I need Help Please???

This is reaally important.

The formula P=Po(1+r)^n gives the population P at the end of an n-year time period, where Po is the initial population and r is the average anual growth rate. The U.S. Population grew from 248.7 million in 1990 to 294.4 million in 2004 (US Census Bureau). Find the average anual rate of growth for the US population for that period.

I have tried the numbers in the formula, but i don't know how to solve it. Quick Responses with the answer is greatly appreciated. Thank You.