Need help on this question for math 11

Hi there i have a link here from tinypic so you could see the question it needs to be answered for me (Giggle)

http://i40.tinypic.com/mcdpxh.jpg

Volume of a pyramid = 1/3 * base area * height. Draw a triangular crosssectiom viewed along one of the base diagonals.You get an isosceles triangle ( two equal pyr legs and the lenght of the diagonal.Take it ftom there,The resr is easy.