6. Given a quadrangular pyramid $P - A B C D$ with a square base of side length 6, the lateral edge $P A \perp$ base $A B C D$ , and $P A = 8$ , then the volume of this quadrangular pyramid is $\_\_\_\_$.
(5 points) As shown in the figure, a point P moves counterclockwise on a circle of radius 2. Its initial position is $P _ { 0 } ( \sqrt { 2 } , - \sqrt { 2 } )$, and its angular velocity is 1. Then the distance $d$ from point P to the $x$-axis as a function of time $t$ has a graph approximately as follows:
6. Given a quadrangular pyramid $P - A B C D$ with a square base of side length 6, the lateral edge $P A \perp$ base $A B C D$ , and $P A = 8$ , then the volume of this quadrangular pyramid is $\_\_\_\_$.\\