The milk factory produced an average of (1/7) tons of milk per day in the first quarter, (1/42) tons per day in the second quarter, and (1/21) more tons per day in the third quarter than in the second quarter. How many tons of milk is produced on average per day?
牛奶厂第一季度平均每天产奶(1/7)吨，第二季度平均每天产(1/42)吨，第三季度比第二季度平均每天多产(1/21)吨，第三季度平均每天产奶多少吨？
<gadget id="calculator">1 / 42</gadget>
<output>1/42 = around 0.02381</output>

<gadget id="calculator">1 / 21</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">(1/42) + (1/21)</gadget>
<output>1/14 = around 0.071429</output>

<result>1/14 = around 0.071429</result>