For this calculation, an opening must provide at least 5.7 square feet of net clear area, at least 20 inches clear width and at least 24 inches clear height. Its clear width is 34 inches. If the selected clear height must be in quarter-inch increments, what is the smallest height that meets all three stated limits?

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why C is correct

Required height from area is (5.7 × 144) / 34 = 24.141176... inches. Round upward to the next permitted quarter-inch increment: 24.25 inches. A 24-inch opening provides only 816 / 144 = 5.6667 square feet. Both stated linear minimums are also satisfied at 34 by 24.25 inches. This checks supplied limits, not the applicability of a particular code exception.