Question 885842
Let {{{y = 5^x}}}

{{{(25^x)-8*(5^x)=-16 }}}
{{{(5^(2x))-8*(5^x)=-16 }}}
{{{(5^x)^2-8*(5^x)=-16 }}}
{{{y^2-8y=-16}}}
{{{y^2-8y+16=0}}}
{{{(y-4)(y-4)=0}}}

{{{y=4}}}
{{{5^x=4}}}
{{{x=log( 5, 4)}}}