Decompose the figure into two rectangles and add the areas.
Find the area of the entire rectangle and of the removed corner and subtract the areas.
Decompose the figure into three rectangles and add the areas.
Step-by-step explanation:
With all of these you can actually calculate the area of the composite figure, some of them are more easy and efficient than the other, for example dividing the composite area into three rectangles is not very efficient but will do the job, and the one where you decompose the area into two rectangles would be the best one, as well as the one where you find the area of the larger rectangle and the subtract from that the rectangle that is taken off in the right corner.
