Skill: Find area of composite rectangles

To find the area of a composite rectangle figure:

1. Split the figure into smaller, non-overlapping rectangles, or find the area of a large rectangle and subtract a missing part.
2. Find each rectangle’s area using

$$\text{Area}=\text{length}\times\text{width}.$$

3. Add the smaller areas, or subtract the missing area.
4. Write the answer in square units.

Example: An L-shaped figure fits inside an $8$-unit by $6$-unit rectangle. A $3$-unit by $2$-unit rectangle is missing from the top-right corner.

Step 1: Find the area of the large rectangle.

$$8\times 6=48\text{ square units}$$

Step 2: Find the area of the missing rectangle.

$$3\times 2=6\text{ square units}$$

Step 3: Subtract the missing area.

$$48-6=42\text{ square units}$$

So, the area of the composite figure is

$$\boxed{42\text{ square units}}.$$

We find area by covering the inside of the figure. Perimeter is different because it measures the distance around the outside.