When will a road reach a certain condition? I have an exponential regression equation that is designed to predict the future condition of a road at a certain age:
condition = 21-EXP(0.06*age)
Note: Road condition is a range from 1 to 20; a road with a condition of 20 is in perfect condition.

Question:
I know that a road has a condition of 9.4.
How many years will it take for the road to reach a condition of 8? Can this be gleaned from the original equation?

Hint #1: Call the equation $$C = 21 - e^{0.06A}$$ How would you solve this in terms of A?
Hint #2: When would the road be in the worst condition?  How many years would this take?
