How did you find the height of the two triangles in the illustration provided in the answer box?

Jason,

It would require a basic knowledge of trigonometry to calculate the heights exactly as laid out in the explanation. Since trig knowledge is not required for the GRE test, the explanation does not do a very good job. Actually we can solve this problem by estimating, based on pictures we draw for extreme conditions.

(i) We know when z=90, the area is 24, so when z=89, the area is very close to 24, which is larger than 15 in Column A.

(ii) When z = 0, the height is very close to 0, say 0.1; then the area is a very small number, which is less than 15. So less than column B.

Hence, D.

Ya, It's ok of the answer D. and I do get same answer through making guess the value oz will vary and hence enough information Is not given. But will you please give a easy clue to found the Height of such problems ?