The area of the colored part of the grid is 24 square units.
What is the area of the colored grid?
If each grid represents 1 units
Area of the colored grid = Length × width
Length = 8 units
Width = 3 units
Area of the colored grid = Length × width
= 8 units × 3 units
= 24 square units
Therefore, Susan colored 24 square units of the decimal grid.