A wall clock takes 6 seconds to strike 4 o'clock, timed from the first stroke to the last. Striking at the same steady rate, how long does it take to strike 8 o'clock?

The time is spent in the gaps between strokes, not on the strokes themselves. Four strokes have 3 gaps between them, so each gap is 6 ÷ 3 = 2 seconds. Eight strokes have 7 gaps, so the striking takes $7\times 2=14$ seconds. The traps: 12 seconds doubles the 6 seconds because the hour has doubled, but the gaps go from 3 to 7, which is not doubling; 16 seconds counts 8 gaps, as though a gap followed the last stroke as well; 10 seconds counts only 5 gaps, one for each extra stroke beyond the first four.