Jaeda, this is the solution to the exercise:
Diameter of the cone = 18 m
Radius of the cone = 9 m (18/2)
Height of the cone = 26 m
Let's recall the formula for the volume of a cone:
Volume of a cone = π * r² * h/3
Replacing by the values we know:
Volume of a cone = 3.1416 * 9² * 26/3
Volume of a cone = 3.1416 * 81 * 8.667
Volume of a cone = 2,205.5 cubic meters