Emilia needs 42 cartons of berries to make a berry cobbler. She already has 2 cartons of strawberries and 7 cartons of blueberries in her cupboard. She decides to go to the supermarket to get more cartons. How many more cartons of berries should Emilia buy?
She previously had 2 cartons + 7 cartons = 
<gadget id="calculator">2+7</gadget>
<output>9</output>
9 cartons of berries.
Emilia needs to buy 42 cartons - 9 cartons = 
<gadget id="calculator">42-9</gadget>
<output>33</output>
33 cartons of berries.

<result>33</result>