Question 730627
speed of boat = x
speed of current = y

{{{120/(x+y) +120/(x-y)= 15}}}...................(1)

{{{120(x-y)+120(x+y) = 15(x^2-y^2)}}}

{{{120x-120y+120x+120y=15(x^2-y^2)}}}

{{{240x=15(x^2-y^2)}}}


{{{120/(x+2y) +120/(x-2y) = 24}}}....................(2)

{{{240x=24(x^2-4y^2)}}}

{{{15(x^2-y^2)=24(x^2-4y^2)}}}

{{{-9x^2=-81y^2}}}

x/y =3, 
x=3y

{{{120/(x+y) +120/(x-y)= 15}}}
substitute x=3y

{{{120/(4y) +120/(2y)=15}}}

120+240=60y
360=60y
y=6 kphthe speed of current
x= 3y 
x= 18kph speed of boat