Chapter R - Section R.3 - Exponents, Roots, and Order of Operations - R.3 Exercises - Page 29: 19

$z^{7}$

In algebra, exponents can be used to write products of repeated factors. Exponents take the form $a^{b}$, where $a$ is the repeated factor and $b$ is the amount of times that the factor is being multiplied by itself. In this case, z is being multiplied by itself 7 times. Therefore, $z\times z\times z\times z\times z\times z\times z=z^{7}$.