Ava planted 9 apple trees in her backyard. That's 3 more than Lily planted in her backyard. How many apple trees did they plant in their backyards collectively?
Lily planted 9-3 = 
<gadget id="calculator">9-3</gadget>
<output>6</output>
6 apple trees in her backyard.
They planted 9+6 = 
<gadget id="calculator">9+6</gadget>
<output>15</output>
15 apple trees in their backyards collectively.

<result>15</result>