Originally Posted by

**zzephod** Take logs of the equation then subsitute the data given into the resulting equation and you will have a pair of simultaneous linear equations in $\displaystyle \log(D_0)$ and $\displaystyle k$ which you can then solve

Alternativly substitue the data into the original equation then divide one of the resulting equations by the other to get:

$\displaystyle \frac{D_2}{D_{5}}=10^{k(2-5)}$

which you can solve for $\displaystyle k$ and then go back to one of the original equations to solve for $\displaystyle D_0$