Let x, y be numbers.
The addition identity property states that 0 + x = x.
The commutative property states that x + y = y + x
If you distribute -5 to the things in the parenthesis you would get 10k-20 which is the same as -5(-2k+4)
The playground is a square, so there will be a right triangle formed by diagonal and two sides. So sides length²*2=diagonal length². So the side length is 38.9 meter.