X would be the amount of days in the week she has to do so. It's just confusing cause during the week so I'm assuming she's not spreading it across the week of 7 days, just the 4.
Given that Mae bought some grapes and used 13 of them. She split apart the remaining grapes into 4 equal parts to eat for snacks each day during the week. We may take each statement in parts. Beginning with Mae bought some grapes and used 13 of them, if the number of grapes she bought is V, then she would have left
= V - 13 grapes
If She split apart the remaining grapes into 4 equal parts to eat for snacks each day during the week it means that each day, she will eat