1CASe 1
no stream velocity
velocity of man = v km/hr
v = 100*15/1000 = 1.5 km/hr . (converting given measurements in km and hr)
CASE 2:
let the stream velocity be 'u' km/hr .
→ resultant velocity perpendicular flow is = √v2-u2
thus , √v2-u2 = 100*12/1000= 1.2
v2-u2 = 1.44
u2 = 2.25 - 1.44 = 0.81
u = 0.9
velocity of the current = 0.9 km /hr or 0.25 m/s