There are three classes in grade six. Classes one and two account for two-thirds of the class, classes two and three account for 13/18 of the class, and class two has 56 students. How many students are there in grade six?
六年级有三个班，一、二班人数占全级的三分之二，二、三班人数占全级的18分之13，二班有56名，六年级有学生多少人？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">13 / 18</gadget>
<output>13/18 = around 0.722222</output>

<gadget id="calculator">(13/18) - 1</gadget>
<output>-5/18 = around -0.277778</output>

<gadget id="calculator">(2/3) + (-5/18)</gadget>
<output>7/18 = around 0.388889</output>

<gadget id="calculator">56 / (7/18)</gadget>
<output>144</output>

<result>144</result>