"A square with a perimeter of 20 cm is inscribed in a square with a perimeter of 28 cm. What is the greatest distance between a vertex of the inner square and a vertex of the outer square, in centimeters?"
I worked out the area of the individual sides- 5 for for the small square and 7 for the big one. I also noticed side $a^2+b^2=25$ (see picture) due to Pythagoraean theorem and that $a+b$ is 7, but I don't know if this helps me at all. Any help is greatly appreciated.