Max should have the other two vertices at (4, 2) and (4, -2) in order to make the area of his garden 20 square feet.
Using the given vertices and the formula for the area of a rectangle,
Area = Length * Width
Given vertices:
A(-1, 2)
B(-1, -2)
The length of the rectangle is the difference in the x-coordinates of the two given vertices, and the width is the difference in the y-coordinates.
Length =

Width =

To find the missing length. Let's call the missing vertices C and D:
Area} = 20 = Length * Width
20 = Length * 4
Length =

To find the missing coordinates, we add 5 to the x-coordinate of the given vertices:
C = (-1 + 5, 2) = (4, 2)
D = (-1 + 5, -2) = (4, -2)
Therefore, Max should have the other two vertices at (4, 2) and (4, -2) in order to make the area of his garden 20 square feet.
Complete question:
Max is drawing plans for a garden, measured in feet, which is shown below on the coordinate plane. Max has two vertices
of the garden at points (-1, 2) and (-1,-2).
At which points should Max have the other two vertices in order to make the area of his garden 20 square feet?