The frustum is cut by a pyramid, so the upper and lower bottom surfaces are similar polygons, and the ratio of their areas is equal to the square of the similarity ratio; The ratio of the height of the whole pyramid to the height of the truncated pyramid is equal to the similarity ratio. According to these basic knowledge, this exercise can be solved as follows:

Let the height of the prism be h, according to the meaning of the question:

35? :(35-h)？ =245:80

Or 35:(35 hours) =7:4

Solve h= 15.

Let the height of truncated frustum be h0.

H0=35-h=20。

∴ frustum volume v = (1/3) [35× 245-20× 80] = 2325.