The answer is 0

In[64]:= 0.3^0
Out[64]= 1.

because the right hand side is 1. More general

In[74]:= Solve[1/0.3^x == 1/817, x, Reals]
During evaluation of In[74]:= Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result. >>
Out[74]= {{x -> -5.56959}}

In[75]:= NSolve[0.3^(-x) == 1/817, x, Reals]
During evaluation of In[75]:= Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result. >>
Out[75]= {{x -> -5.56959}}

In[76]:= Rationalize[0.3^(-x) /. %75[[1, 1]]]
Out[76]= 1/817