My dog was born when I was 15 years old. Two years from now, my dog will turn 4 years old. How old am I now?
In 2 years, my dog will be 4 years old, so my dog is 4 - 2 = 
<gadget id="calculator">4-2</gadget>
<output>2</output>
2 years old now.
So I am 15 + 2 = 
<gadget id="calculator">15+2</gadget>
<output>17</output>
17 years old now.

<result>17</result>