Need to know the answer to the question

To find the area of this irregular shape, you divide it up into regular shapes and find the area as if it was a regular rectangle. Length times width. So first you would do 40 times 30 which is 1200. Then you would do 20 times 24, which is 480. Where did I get twenty four? I subtracted 40 from 64 to get the missing length. Lastly, we add 480 and 1200 to get 1680. That's the area. 1680.