Angelina is 4 years older than Justin is now. In 5 years, Angelina will be 40 years old. Calculate the age of Justin currently.
In five years, Angelina will be 40 years old, meaning currently she is 40-5 = 
<gadget id="calculator">40-5</gadget>
<output>35</output>
35 years old.
Since Angelina is 35 years old right now, and she is four years older than Justin, it means Justin is 35-4 = 
<gadget id="calculator">35-4</gadget>
<output>31</output>
31 years old.

<result>31</result>