Answer
-5
Work Step by Step
You have the expression ($b^{-4}$$)^{x}$=$b^{20}$.You have to find the value of x:
$b^{-4x}$=$b^{20}$ -multiply the exponents because you are raising a power to a power.
-4x=20 -divide both sides by -4-
x=-5
The expression would be ($b^{-4}$$)^{-5}$=$b^{20}$
