1-3-4-Funny calculation formulas, written on the label

Alice’s Story
Alice took to hand the bottle label that says “marmalade”.
But because it was empty, she would be very disappointed.

Because she did not want to hurt the people who are under, dropping the bottle it was disgusting. So while she fell, she put it in another cupboard.

Then, she found a bottle of formula is written on the label. But the formula is wrong. She has a calculation to hard.

Alice is excited because She wanted to solve the mystery of this formula.

• [4]+[2]=[12]
• [8]+「3]=[19]
• [6]+「5]=[28]
• [2]+[4]=[?]