.
Two smaller right-angled triangles are similar, which gives the proportion
=
.
It implies
(8-x)*(6-y) = xy,
48 - 6x - 8y + xy = xy,
48 = 6x + 8y,
3x + 4y = 24.
So, you have these two equations
3x + 4y = 24, (1) and
xy = 12. (2)
From (1), express x =
and substitute it into (2). You will get
a quadratic equation, which you can easily solve (by any method you know).
I will leave the details to you.
Answer. x = 4 cm, y = 3 cm.