Verified Answer :

\(f(x)=\log_4x\\\\ y=\log_4x\\ x=4^y\\ f^{-1}(x)=4^x\)

\(f\left( x \right) =\log _{ 4 }{ x } \\ \\ \log _{ 4 }{ x } =y\\ \\ { 4 }^{ y }=x\\ \\ \therefore \quad { f }^{ -1 }\left( x \right) ={ 4 }^{ x }\)