Dad is a years old this year, and is 2 years older than mom. The formula to express mom's age next year is a-how much
爸爸今年a岁，比妈妈大2岁，表示妈妈明年岁数的式子是a-多少
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>