Doubt from River man problem

image IN QUESTION 16 i have a doubt how to select the velocity of man with respect to ground as in some question it is along the y axis and in some questions it is not along the y axis

River velocity=u
Man velocity=v
Let
man make angle (theta) with perpendicular to the direction of
flow of river ( in your language y axis) now use sine rule of properties of triangle
u/sin(theta)=v/sin(90 degree)
Sin(theta)=u/v=2/3

Here destination vertically opposite ...so if swim perpedicular
to the direction of flow of river(in your language) hecan never
reach destination but get drifted away...

Sir i dont know this property of triangle can you explain me by some other method

Ok i shall try...

@Raghuveer_2021 what @Tanmay_1 sir did is right.
I am adding a little bit explanation oriented

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Thankyou sir i got it