To solve the function in terms of x:
[tex]\log _{4^x}2^a=3[/tex]
find the power of the subscripts of the log
[tex]\begin{gathered} \log _{4^x}2^a=3 \\ \log _{2^{2x}}2^a=3 \\ \frac{a}{2x}\log _22=3 \\ \text{where }\log _22=1 \\ \frac{a}{2x}=3 \end{gathered}[/tex]
cross multiply the expression
[tex]\begin{gathered} \frac{a}{2x}=3 \\ a=3(2x) \\ a=6x \end{gathered}[/tex]
Therefore the correct answer of a = 6x
