There are many chemical changes in daily life, such as 3A+2B=2C+D. A and B represent the old substances before the change, and C and D represent the new substances produced after the change. It is known that before and after the chemical change, the total mass of old substances must be equal to the total mass of new substances. The mass ratio of the two old substances A and B participating in the change is 3:4. If the total of new substances C and D produced is 140 grams, what is the mass of substance B participating in the change?
日常生活中有许多化学变化，如3A+2B=2C+D．A、B表示变化前的旧物质，C、D表示变化后产生的新物质．已知在化学变化前后，旧物质的总质量一定等于新物质的总质量．A、B两种旧物质参加变化时的质量比为3：4，若产生的新物质C和D共140克，则参加该变化的B物质的质量为多少？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">140 * (4/7)</gadget>
<output>80</output>

<result>80</result>