I have a question asking to a.) find the first quartile of an exponential distribution and b.) seeing how far it is below the mean.

I get the integral of my distribution $\displaystyle \frac{1}{\theta }e\left( -\frac{x}{\theta } \right)$

and get

$\displaystyle -e\left( -\frac{x}{\theta } \right)$

from a previous section i see that to find the first quartile, you solve F(x)=.25

(in my book they use the notation F(pi sub .25)=.25

To solve i try to ln both sides which doesnt work since i have a negative number, so im doing something wrong. Anyone know howe i strayed? Thanks!