can someone please explain how to do this?

Answer:
7.07 units or cm or whatever
Step-by-step explanation:
so the area is 25 and it's a square so each side of the small square must be 5 units. Split the small square in half to make two triangles. Using one triangle you know it's a right angle triangle and has two side lengths of 5 units. To find the hypotenuse of the triangle do Pythagoras 5^2 + 5^2 = 50 √50= 7.07