<PRE><B>Question 588188</B>
Boat speed = xmph
current speed = 4mph

sped with current = x+4 mph
speed against current = x-4 mph


t= d/r
time taken with current = 
40/(x+4) 

time taken against current = 40/(x-4)

40/(x-4) =40/(x+4) + 16

40/(x-4) -40/(x+4) =16

LCD = (x+4) (x-4)

multiply by the LCD

40(x+4) -40(x-4) = 16(x^2-16)

40x+160-40x+160 = 16x^2-256

16x^2= 320 +256
16x^2=576
x^2= 576/16
x^2= 36
x= +/- 6

speed of boat = 6 mph
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