It is stipulated that 10 tons is recorded as 0 tons, then 12 tons is recorded as +2 tons, then +5 tons indicates the actual number of tons.
规定10吨记为0吨，则12吨记为+2吨，那么+5吨表示实际多少吨．
<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<result>15</result>