jmc

The two bases of the trapezoids are the segments $AB$ and $CD$, and the height is the perpendicular distance between the bases, which in this case is the difference of the $x$-coordinates: $5-1=4$. Similarly, the lengths of the bases are the differences of the $y$-coordinates of their two endpoints. Using the formula $A=\frac{1}{2}(b_1+b_2)h$, the area is $\frac{1}{2}(3+6)(4)=\boxed{18}$ square units.