Add 20% of a number to the quotient of 84 divided by 42, and the sum is 4.5. What is this number?
一个数的20%加上84除42的商，和是4.5．这个数是多少？
<gadget id="calculator">42 / 84</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4.5 - (1/2)</gadget>
<output>4</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4 / (1/5)</gadget>
<output>20</output>

<result>20</result>