A tank truck is full of oil and weighs 10 tons. After half of the fuel is used up, the weight of the truck is 6 tons. How many tons does the empty truck weigh?
一辆油罐车装满了油，连车重10吨，用去一半油后连车重6吨，这辆空车重多少吨．
<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<result>2</result>