Question 866614
{{{b^x=y}}}    means {{{log(b,y)=x}}}

you are given: {{{5^(-3x)=4}}} 

in your case {{{b=5}}}, {{{x}}} is actually {{{-3x}}}, and {{{y=4}}}


so you have {{{log(5,4)=-3x}}}


{{{log(5,4)/-3=x}}}............in base {{{10}}}, {{{log(5,4)}}} will be {{{log(4)/log(5)}}}


{{{( log(4)/log(5))/-3=x}}}


{{{- log(4)/3log(5)=x}}}