Answer:
48 sq. in.
Explanation:
Different figures (rectangular prisms, cylinders, triangular prisms etc.) have different volume formula. But what formula of "volume" do they come from??
It is:
Volume = Area of Base * Height
Note: we didn't specify any Area of Base formula because it depends. If base is circle, the area is different than if base was suppose a square. But this is the general formula of volume.
Now,
Given
Height = 18 inch
Volume = 864 cubic inch
We can write:
Volume = Area of Base * Height
864 = Area of Base * 18
Thus,
Area of Base = 864/18 = 48 sq. in.
This is what we are wanting, "area of base" (irrespective of the shape).