30 men working 8 hours per day can dig a pond in 16 days. By working how many hours per day can 32 men dig two same ponds, in 20 days?

Total work = 30×8×16 = 3840 man-hours (for 1 pond). For 2 ponds = 7680 man-hours. With 32 men in 20 days: hours/day = 7680/(32×20) = 7680/640 = 12. That exceeds options; rechecking: 30×8×16=3840 per pond, 2 ponds=7680. 32×20×h=7680 → h=12. Answer key gives (d) 8 hours, suggesting 1 pond scenario or different reading.