#### Answer

x

#### Work Step by Step

We are given the expression $9x^{5}$.
Recall that an exponential expression consists of a factor, known as the base, and an exponent. The number of times that the base is multiplied is indicated by the value of the exponent.
Therefore, x is the base of the exponent 5.
Multiplied out, $9x^{5}=9(x\times x\times x\times x\times x)$