Given the following equation:
[tex]4^x=9[/tex]You can identify that the left side of the equation has this expression:
[tex]4^x[/tex]Where the base is:
[tex]4[/tex]And the exponent is a variable:
[tex]x[/tex]By definition, the equations whose variables are contained in the exponents, are called "Exponential Equations".
Hence, the answer is: Option a.