Volume of a rectangular pyramid:
[tex]V=\frac{1}{3}(L\cdot W)\cdot h[/tex]Volume of a rectangular prism:
[tex]V=L\cdot W\cdot h[/tex]As you can see the volume of a rectangular pyramid (y) is a thrid part of the volume of a rectangular prism (x). Then, if the length, width and height of both molds is the same the volume of the rectangular prism (x) is three times the volume of the volume of the rectangular pyramid (y).
[tex]\begin{gathered} x=3y \\ y=\frac{1}{3}x \end{gathered}[/tex]