Answer:12.5 hoursStep-by-step explanation:The situation:2000: LInflow Rate: 2000 L/6.25 hr or 320 L/hrOutflow Rate: -2000 L/12.5 hr or -160 L/hr==We can calculate a net flow rate when both pipes are open at the same time:(320 L/hr) + (-160 L/hr) = 160 L/hrAt 160 L/hr, an empty 2000L tub will fill in (2000 L)/(160 L/hr) = 12.5 hours