Answer
x=-3
Work Step by Step
In the exponential functions a given value of x leads to exactly one value of $a^x$, thus we can rewrite the equation:
$4^x=8^{x+1}$
$4^x = (2^2)^x= 2^{2x}$
$8^{x+1}= (2^3)^{x+1}= 2^{3\times (x+1)}=2^{3x+3}$
So,
$2^{2x}=2^{3x+3}$.
$2x=3x+3$
$-3=x$
