Mom gave Xiaohong 20 yuan, and Xiaohong bought a pair of shoes for 18 yuan. There is still 15 yuan left on her body, how much yuan does Xiaohong have on her body?
妈妈给了小红20元钱，小红买了一双鞋子花了18元．身上还剩下15元，小红身上原有多少元？
<gadget id="calculator">18 - 20</gadget>
<output>-2</output>

<gadget id="calculator">15 + (-2)</gadget>
<output>13</output>

<result>13</result>