A launch (18 km/h in still water) must go 60 km upstream on a 3 km/h current. After 2 hours its engine fails and it drifts for 30 minutes. Repaired, it then manages only half its still-water speed. How long does the whole journey take?

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7 h 45 min. After 2 h: 30 km up. Drifting 0.5 h takes it back 1.5 km ⇒ 28.5 km done, 31.5 km left. New upstream speed = 9 − 3 = 6 km/h ⇒ 5.25 h. Total = 2 + 0.5 + 5.25 = 7.75 h = 7 h 45 min.

A launch (18 km/h in still water) must go 60 km upstream on a 3 km/h current. After 2 hours its engine fails and it drifts for 30 minutes. Repaired, it then manages only half its still-water speed. How long does the whole journey take?

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