Answer: I don't think any of them were challenging alone. But when I had to reflect an image on the y axis, while translating it and rotating it... that was the hardest. If I had to say one alone, it would probably be reflecting. Not hard, but the hardest of them all. An example of where you could find the transformation in the real world could be in a mirror, on a butterfly's wings, or even a pizza. The symmetry of those things are reflecting each other perfectly. (well, maybe not the pizza always.)
Explanation: