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.
To find how much the total would be with tax, you use this equation x=item price 0.06x+x when you pit in in the equation, it would be 0.06×28+28 which equals 29.68