GMAT Quantitative Reasoning Practice Test 1

First draw the $\mathit{x}$ - and $\mathit{y}$-axes, then plot the points and connect them. The length of the base is 6 units [from $\left(6,3\right)$ to $\left(6,-3\right)]$ and the height is 2 units [from $\left(6,0\right)$ to $\left(4,0\right)]$.
Area of a triangle $=($ base $\times$ height $)/2$, so $\left(6\times 2\right)/2$ is 6 .