Magic Music Visuals

Hello, I would like to combine multiple scenes next to each other, with a mask on top of it.
Let's say I have 3 triangles next to each other (this is the mask), and in every triangle I have another scene going on.
Is this possible? The mask can be placed in Post Processed scene, but how about placing the scene next to each other?
Thanks in advance

Simples!

if you see it, it looks obvious. i'll try that tomorrow!