The right-hand side can be simplified to x/2. By doubling, we can get rid of the fraction:
4x4^3x=x. Assuming this is meant to be: 4x(4^3x)=x then we have x(4*4^3x-1)=0 and x=0 is a solution. The other solution is 4^3x=1/4. Take logs to the base 4: 3x=-1 so x=-1/3.
Alternatively, we can write 4*4^3x-1 as 4^(3x+1)-1, so 4^(3x+1)=1 and 3x+1=0, giving x=-1/3.