If one of a right measures 3 centimeters and the other leg measure 6 centimeter, what is the length of the hypotenuse in centimeters?

I'm confused on this could anyone me and show me what i need to do to solve it.

Rachel is baking a cake but does not know if she wants to make a round or a square cake which cake has a larger area a round 8 inch cake or a square 9 inch cake

Given a circle with measures of (c, d, and r) and a circle with measures of (c', d', and r'), find r' if c c' = 0.25 and d = 6.0. a. 6 b. 12 c. 18 d. 24