Boat very good question with a special way

P, Q, R are three towns on a river which flows uniformly. Q is equidistant from P and R. A man rows from P to Q and returns in 10 h. He can row from P to R in 4 h. The ratio of speed of the man in still water to the speed of the current is :
(a) 5 : 3
(b) 3 : 5
(c) 2 : 5
(d) 1 : 2
(e) None of these

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A does half as much work as B in three-fourth of the time. If together they take 18 days to complete the work, how much time shall B take to do it?

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