Suppose that the man takes H hours to cover 4 km downstream and H house to cover 3 km upstream.
Then, 48H/4 + 48H/3 = 14
⇒ H = 1/2
∴ Rate upstream = 3/(1/2)= 6 km/hr
and rate downstream = 4/(1/2) = 8 km/hr
∴ Rate of the stream = (8 - 6)/2 = 1 km/hr .