Mark and Dora divorced last year on April 1.  Ben is their 10 year old son.  Ben lived with Dora after the divorce until August 17,  He then moved in with mark for the rest of the year.  Mark's AGI was $75,000, and Dora AGI was $55,000.  Dora's mother stayed with Ben at Dora's house for four days in July when Dora went on a business trip.  Ben the stayed at a friend's house for five nights in July.  Which of Ben's  parents is the custodial parent for purposes of claiming Ben as a Qualifying child?