Im assuming the 18 inches is either the diameter or the radius.
If it is the diameter, then the equation will be π * d or 3.14 * 18
If it is the radius then the equation will be π * r or 3.14 * (18 * 2)
Equation 1 = 56.59
Equation 2 = 113.04
When multiplying by Pi however, you will never get a real answer as Pi is an irrational number (It's digits are infinite). So the correct way to write that (unless the question asks you to simplify it down as much as I have) is 18π or 36π
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