A straight rod is embedded in a solid rectangular block made of
translucent plastic. Label three of the faces that meet at a corner
A, B, and C.
When the sun is directly overhead, face A of the block is
placed on level ground. The length of the shadow of the rod is 5 units.
When face B is placed on the ground the shadow's length is
6 units and when the face C is placed on the ground, the shadow's
length is 7 units.
How long is the rod?