An architect is making a floor plan for a rectangular gymnasium. The distance between opposite corners of the gym will be 30 meters and the width will be 18 meters. What will be the length of the gym?

The length is: 24 meters

Here's why

So the hypotenuse theory or aka A^2 + B^2 = C^2 lets us know this:

A = 18

B = What we are looking for

C = 30

So before we apply these we're going to do some magic:

B = sqrt (-A^2 + C^2)

Now just put in the numbers

B = sqrt (-18^2 + 30^2)

B = sqrt (576)

B = 24 meters

30^2=A^2+18^2

900=A^2+324

900-324=A^2

576=A^2

24=A

Length is 24 meters