The area of Liam's circular garden can be calculated using the formula for the area of a circle, which is given by:
Area = π * radius^2
In this case, the diameter of the garden is 18 feet. The radius can be calculated by dividing the diameter by 2:
Radius = 18 feet / 2 = 9 feet
Substituting the radius into the formula, we get:
Area = π * (9 feet)^2
= π * 81 square feet
Therefore, the area of Liam's garden is 81π square feet, where π represents the mathematical constant pi.