For a fishing boat, the fishing tonnage in the second half of the month is the same as in the first half (9/10), and the fishing tonnage in the second half of the month is 4.2 tons less than that in the first half. How many tons are fished in the second half of the month?
一条渔船，下半月捕鱼吨数是上半月的(9/10)，下半月比上半月少捕鱼4.2吨，下半月捕鱼多少吨？
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4.2 / (1/10)</gadget>
<output>42</output>

<gadget id="calculator">42 - 4.2</gadget>
<output>37.8</output>

<result>37.8</result>