40% of a number is 120 less than (7/10) of this number, what is this number? (solution by equation)
一个数的40%比这个数的(7/10)少120，这个数是多少？(用方程解)
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">120 / (3/10)</gadget>
<output>400</output>

<result>400</result>