Leon verified that the side lengths 21, 28, 35 form a pythagoreom triple using this procedure

21, 28, and 35 are multiples of 7. So you can divide each number by 7 (in other words scaling the triangle down by a scale factor of 7).
It becomes 3,4,5, which is the base Pythagorean triple.
3^2 + 4^2 = 5^2
9 + 16 = 25

It’s 5 points actually