What are the original dimensions of the square piece of paper?

Answer:
6root2 × 6root2
you have to use pythagoras
a²+b²=c²
c=12
12²=144
a²+b²=144
but it is a square so I'll just change a and b to x because it shows they are equal
x²+x²=144
2x²=144
x²=72
x=6root2