Question 347407
let speed of current be xmph
downstream speed = x+4 mph
upstream speed = 4-x mph

Time downstream = 12/(x+4)
Time upstream = 12/(4-x)
....
12/(x+4)+12/(4-x)=8
LCD = (x+4)(4-x)
12(4-x)+12(x+4)/(x+4)(4-x)=8
-12x+48+12x+48 = 8(16-x^2)
96=128 8x^2
8x^2=128-96
8x^2=32
x^2=4
x= 2 mph the current speed.