Question 948326
Equations are 
log(y,x)=3,log(y,(4x))=5
as rendered become the system
{{{system(log(y,x)=3,log(y,(4x))=5)}}}



The second equation is {{{log(y,4)+log(y,x)=5}}}.
Substitute using the first equation for {{{log(y,x)}}};


{{{log(y,4)+3=5}}}
{{{log(y,4)=2}}}
put into exponential form,
{{{y^2=4}}}
{{{highlight(y=-2)}}} or {{{highlight(y=2)}}}.