How many grafts will it take to fill in this area?

To answer the question of how many grafts it will take, I will have to know the thickness of your hair (fine, medium or coarse). The range therefore would be 2,700 for fine, 2,300 for medium and possibly 2,000 for coarse hair. From the photo, it is evident that you are balding behind the line you drew, so extra grafts should be considered for this area depending on how far back it goes.