There are three classes in the sixth grade in our school, among which the number of students in class one and class two account for the whole grade (2/3), and the number of people in class two and class three takes up the whole grade (13/18). It is known that there are 56 students in class two, please complete Number of grades?
我校六年级有三个班，其中一班与二班的人数占全年级(2/3)，二班与三班人数占全年级的(13/18)，已知二班有56人，求全年级的人数？
<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>