solving an exponential growth equation using excel

I am trying to write an equation which solves for the amount of years remaining of natural gas resources, based on total proved reserves and annual consumption rates. I need to solve for potential annual growth rates of 0,1,2,3, and 5 percents. 0 is easy, just divide the total reserves by the annual consumption. But when I write an equation to solve the rest of them I get more years remaining, even though the annual consumption rate is increasing.
I tried by using the equation:
t=(ln(R/A))/(ln(1+i))
where t=time remaining in years, R=total reserves,A=annual consumption,and i=annual growth rate as a decimal.
I believe that the problem is that it isn't including the annual consumption for every year, but I'm not sure how to make it do that.

Any help would be awesome.
Thanks