Final answer:
The variable expression is 15 / (x * 18).
Step-by-step explanation:
The variable expression for the given phrase is: 15 / (x * 18).
Here, 'x' represents the unknown number. The phrase can be broken down into two parts:
- The product of a number and 18, represented by x * 18.
- The quotient of 15 and the above product, represented by 15 / (x * 18).
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