Use the idea of similar triangles to get the ratio of the lengths first.

There are 3 similar triangles. You've already drawn the cross section, so you know the ratio of height is 1 : 3 : 6

(Height of smallest one = h, medium one = 2h + h = 3h, biggest one = 3 h + 2h + h = 6 h)


Now, do you see 3 different sized right pyramids ? They are similar pyramids (their sides are all similar triangles and the base are all squares)

Since the ratio of the height is 1 : 3 : 6,
the ratio of their volume is 1³ : 3³ : 6³ = 1 : 27 : 216


C known as a frustum. It is just the largest pyramid - the medium pyramid.

so ratio of volume of A to C = 1 : (216 - 27)
= 1 : 189

thank you