The Answer is 12.5 hours or 750 mins. H stands for hours and V stands for vases. you are given that 2h = 8v. 1H = 4v; Then 30 mins = 2v; Finally 15 mins= 1v. keep dividing the time until you are left with 1 vase. So then Once you find the time per vase you Multiply by 50. which is 750 mins and if you're want it in hours divide by 60.