Answer
A good phrase to use would be: "9 less than the quotient of z and 8."
Work Step by Step
We are given the expression: $\frac{z}{8}$-9. Because the expression tells us that we are subtracting 9 from $\frac{z}{8}$, we write "9 less than." We next denote the division of z and 8 by using the phrase "the quotient of z and 8," being careful to list the numerator (the top of the fraction, which in this case is z) first and the denominator (the bottom of the fraction, which in this case is 8) second. Furthermore, a good phrase to use would be: "9 less than the quotient of z and 8."
