Since the relationship is directly proportional,
Abigail prepared 15 kilograms of dough after working 3 hours.
Let us calculate the number of dough he prepared in 1 hour,

Therefore, she prepares 5kg of dough in one hour.
Hence, the amount of dough she will prepare in 4hours will be

Therefore, Abigail will prepare 20kg of dough in 4 hours.