Awindow in a house is in the shape of a square. the side length of the window is 20 inches. what is the length of the diagonal from one corner of the window to the opposite corner? round your answer to the nearest tenth

A Square Window would have four equal sides. So you would use the Pythagorean Theorem (a²+b²=c²) to solve the problem. so it would be set up like this; 40²+40²=c². then you would evaluate it and it become:
400+400=c²
800=c²
√800=√c²
28.3 inches

Ithink it's the first one ( let me know if it right)