Taking the last equality on your second line:
You can simplify like this:
Another way of thinking of it is to solve the following for x:
to get .
Then, instead of using 1.3 as your base, use
It may seem strange to leave your answer in this form, without simplifying the e to the "ln" power, but there could be a variety of reasons for it. For example, now you know that is the rate of decay in a continuous decay model.