Answer:
18 inches
Explanation:
Volume of a pyramid is:
V = ⅓ Ah
where A is the area of the base, and h is the height of the pyramid.
The base is a rectangle. Area of a rectangle is width times length, so:
V = ⅓ wlh
Plugging in values and solving:
1512 = ⅓ w (21) (12)
w = 18
The width of the base is 18 inches.