There were 85 boxes of chalk in the school, and another 56 boxes were bought. 73 boxes have been used up, how many boxes are left?
学校里原有85盒粉笔，又买来56盒．用去了73盒，还剩多少盒？
<gadget id="calculator">56 - 73</gadget>
<output>-17</output>

<gadget id="calculator">85 + (-17)</gadget>
<output>68</output>

<result>68</result>