What is the area of the quadrilateral with vertices at (-1, 0), (2, 0), (2, 5), and (-1, 5) ?

There are two sets of Y values identical (0 and 5).

There are two sets of identical X values (-1 and 2)

This makes a rectangle.

The length is 5-0 = 5

The width is 2 - - 1 = 3

Area = Length x width = 5 x 3 = 15 square units.