Question 99644
40=4(s+c) or 40=4*10 or (s+c)=10
40=10(s-c) or 40=10*4 or (s-c)=4
(s+c)=10
(s-c)=4 now add
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2s=14
s=14/7
s=7 speed of the boat 
7+c=10
c=10-7
c=3 speed of the current.