The two brothers rode bicycles from place A to place B at the same time. My younger brother is 4 kilometers per hour in the first half and 6 kilometers per hour in the second half. My brother travels in stages. He traveled 4 kilometers per hour in the first 1/3, 5 kilometers per hour in the middle 1/3, and 6 kilometers per hour in the last 1/3. As a result, my brother arrived 20 minutes before my brother. Q: How many kilometers is it between A and B?