14. Let $v_{1}, \ldots, v_{d}$ be vectors in $\mathbb{R}^{d}$ and define $$ D=\left\{t_{1} v_{1}+\cdots+t_{d} v_{d} \mid 0 \leq t_{j} \leq 1 \text { for all } j=1, \ldots, d ight\} $$ Prove that $D$ is a Jordan region and calculate its volume in terms of the vectors $v_{1} \ldots . . v_{d} .$ CS.VS. 1586||