A, B, and C jointly produced a batch of parts, A produced 30% of the total, and the ratio of the number of pieces produced by B and C was 3:4. Given that C made 20 pieces, how many pieces did A make?
甲、乙、丙三人共同制作了一批零件，甲制作了总数的30%，乙、丙制作的件数之比是3：4．已知丙制作了20件，则甲制作了多少件．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 20</gadget>
<output>35</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">35 / (7/10)</gadget>
<output>50</output>

<gadget id="calculator">50 * (3/10)</gadget>
<output>15</output>

<result>15</result>