Hint: plug in $t:=a\cdot x$ for a new unknown $x$. This simplifies the equation a bit and (provided I didn't make a computation error) if you plug in $a=\ln(4)$ and then try some small integers for $x$ you will find a solution.
Edit: You already found $x^2*e^{a/x}+e^{ax}-12*x=0$. Now plug in $a=\ln(4)$ gives $$x^24^{1/x} + 4^x = 12x$$
Pluggin in $x=2$ gives a solution.
Note that this uses being lucky with your specific equation. If you replace the $12$ by a $13$ I don't think there is any way to solve this algebraically.
Hint: plug in $t:=a\cdot x$ for a new unknown $x$. This simplifies the equation a bit and (provided I didn't make a computation error) if you plug in $a=\ln(4)$ and then try some small integers for $x$ you will find a solution.
Edit: You already found $x^2*e^{a/x}+e^{ax}-12*x=0$. Now plug in $a=\ln(4)$ gives $$x^24^{1/x} + 4^x = 12x$$ Pluggin in $x=2$ gives a solution.
Note that this uses being lucky with your specific equation. If you replace the $12$ by a $13$ I don't think there is any way to solve this algebraically.