If there are 6 adults in the class and Mary wants to give 5/8 of a doughnut to each person, then the total number of doughnuts needed will be:
6 x 5/8 = 3.75
Since we cannot have a fraction of a doughnut, Mary will need to round up to the nearest whole number of doughnuts. Therefore, she will need 4 doughnuts to give each person 5/8 of a doughnut.