Let the speed of the boat in still water be x km/hr and the speed of the stream but y km/hr. Then,Speed upstream =(x−y)km/hrSpeed downstream =(x+y) km/hrNow, Time taken to cover 32km upstream = x−y32 hrsTime taken to cover 36 km downstream = x+y36 hrsBut, TOTAL time of journey is 7 hours.∴ x−y32 + x+y36 =7 ..(i)Time taken to cover 40KM upstream = x−y40 Time taken to cover 48 km downstream = x+y48 In this case, total time of journey is given to be 9 hours.∴ x−y40 + x+y48 =9 (ii)PUTTING x−y1 =u and x+y1 =v in equations (i) and (ii), we get32u+36v=7⇒32u−36v−7=0 ..(iii)40u+48v=9⇒40u−48v−9=0 ..(IV)Solving these equations by cross-multiplication, we get36×−9−48×−7u = 32×−9−40×−7−v = 32×48−40×361 ⇒ −324+336u = −288+280−v = 1536−14401 ⇒ 12u = 8v = 961 ⇒u= 9612 and v= 968 ⇒u= 81 and v= 121 Now, u= 81 ⇒ x−y1 = 81 ⇒x−y=8 ..(v)and, v= 121 ⇒ x+y1 = 121 ⇒x+y=12 ..(vi)Solving equations (v) and (vi), we get x=10 and y=2Hence, Speed of the boat in still water =10 km/hrand Speed of the stream =2km/hr.