A solid cone of base radius 20 cm and height 35 cm is cut by a plane parallel to its base, 14 cm above the base. Find the radius of the circular cut.

The cut is 35 - 14 = 21 cm below the apex, and radii grow in proportion to the distance from the APEX. Radius = $\frac{21}{35}\times 20=12$ cm. 8 cm uses $\frac{14}{35}\times 20$, measuring from the wrong end; 20 cm is the base radius, which the cut cannot equal; 14 cm just repeats the given height.