Question 433043
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Hi
Let c represent the speed of the current
Question states*** time is the same Note: t = D/r 
1.5/(6+c) = 1/(6-c)   |cross Multiplying
   6 + c = 1.5(6-c)
      2.5c = 3
         c = 1.2kmph

CHECKING our Answer***
   1.5/7.2 = 1/4.8 = .2083hr  

As to Your further question:
     A. {{{(3/8x)/(5/12x)}}}  = (3/8x)(12x/5)= 36/40 = 9/10
     B. 4/15y/12/5y = (4/15y)(5y/12) = 1/9