Question 314467
Let the rate of man in still water = x Km/Hr

Hence, downstream speed of themn = (x+2) km/hr and upstream is (x-2) km/hr
As per the problem

30/(x+2) + 30/(x-2)=8
or 30(x-2)+ 30(x+2)=8(x+2)(x-2)
or 60x=8x^2-32
or 8x^2-60x-32=0
or 2x^2-15x-8=0
or (x-8)(2x-1)=0

hence, x=8 or 1/2 < 2  (speed of the river stream), which is not possible.
Hence, Rate of man in still water =8 km/hr