A bookshelf has three volumes, 126 volumes on the upper level, 157 volumes on the middle level, and 90 volumes on the lower level. Please ask a mathematical problem and choose an appropriate method to solve it.
一个书架有三册，上层126本，中层157本，下层90本，请提出一个数学问题，并选择合适的方法解决它．
<gadget id="calculator">126 + 157 + 90</gadget>
<output>373</output>

<result>373</result>