Answer
The answer is as follows. 
Katrielle and the Millionaires' Conspiracy walkthrough
Puzzle Location: Reception area (PC Beate)
Here we have a board made up of lots of small regular triangles.
If you cut the board in two, you can put the two pieces together to make one big regular triangle.
Touch the joins between triangles to draw a line showing where to cut.
You are not allowed to flip eigher of the pieces over.
When the big triangle is put together, the length of each side is equivalent to four tiles.
The cut is a simple one.
You just need to draw a straight line in the right place.
The smaller piece contains five tiles.
Draw a line so that the bottom-right section of the board will be cut off.
The answer is as follows.