check the picture below.
keeping in mind that the volume of a pyramid is one third "area of its base" times its height.
well, notice, the base triangle has itself a base of 10, and a height of 18,
[tex]\bf \textit{volume of a pyramid}\\\\
V=\cfrac{1}{3}Bh~~
\begin{cases}
B=area~of\\
\qquad its~base\\
height\\
-------\\
B=\frac{1}{2}(10)(18)\\
h=14
\end{cases}\implies V=\cfrac{1}{3}\left[ \frac{1}{2}(10)(18) \right](14)
\\\\\\
V=(30)(14)\implies V=420[/tex]