The art class first bought 42 boxes of brushes, distributed 29 boxes to the students, and bought another 27 boxes. How many boxes of brushes are there in the art class now?
美术班先买来42盒画笔，发给同学们29盒，又买来27盒．现在美术班有多少盒画笔？
<gadget id="calculator">42 - 29</gadget>
<output>13</output>

<gadget id="calculator">13 + 27</gadget>
<output>40</output>

<result>40</result>