Geometry pt. 2 help. Thank you!

A cow is tied to the long side of a barn 10 feet from the corner. The rope being used to tie the cow to the barn is 21 feet long. The barn measures 11 feet wide and 28 feet long, what is the total area of the space in which the cow can graze?

You may wish to draw a picture to help in solving this problem. You may include a scanned image of your picture if you feel this will help you explain your work.