The construction of a canal is planned to require 70 people to dig soil and 50 people to transport the soil, but the actual number of diggers is three times that of the soil transporters. How many people will be transferred from the soil transporters to dig the soil?
修一条水渠计划需70人挖土，50人运土，而实际上挖土人数是运土人数的3倍，问从运土的人中调多少人去挖土？
<gadget id="calculator">70 + 50</gadget>
<output>120</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<result>20</result>