Xiao Li is 15 years old this year, and Xiao Ming is 17 years old this year. When the sum of their ages is 50, how old is Xiao Li?
小力今年15岁，小明今年17岁，当两人岁数的和是50岁时，小力是多少岁．
<gadget id="calculator">17 - 15</gadget>
<output>2</output>

<gadget id="calculator">50 - 2</gadget>
<output>48</output>

<gadget id="calculator">48 / 2</gadget>
<output>24</output>

<result>24</result>