Heba ate 1/12 of a box of cereal now the box is 3/4 full what fraction of a full box was there before heba ate it

5/6.

Step-by-step explanation:

If Heba ate 1/12 of a box of cereal and the box is now 3/4 full, then before she ate the box is 3/4 plus the 1/12 (because, in the "before" situation she hasn't eaten yet). So, we need to add the "now" quantity and the quantity eaten:

Then, before she ate the cereal, the box is 5/6 full.