pai
primul robinet curge 13 minute, adica curge in bazin 13×32dal=416dal=4,16kl
al doilea robinet curge 15 minute, adica curge in bazin
15×4hl=60hl=6kl
in bazin mai avem nevoie de 80kl-4,16kl-6kl=69,84kl=6984dal
deci al treilea robinet va curge 6984:9=776 minute(12 ore si 56min)
