There are two walls, one wall is six metres tall, the other wall is four metres tall. A rope is stretched from the top of each wall to the bottom of the other wall - assume that the ropes are so taught that they form straight lines.
How far from the ground is the point where the two ropes cross?
The ropes cross above a point that is 4x from the lower wall and 6x from the taller wall, making the distance between the walls 10x.
This gives two similar triangles: one with sides of 6 and 10x and the other with sides of h and 4x, giving:
h / 4 = 6 / 10, so 10h = 4 x 6, so 10h = 24 and h = 2.4
The intersection is 2.4 metres above the ground.