The ratio of A to B is 3:5, and the ratio of B to C is 4:7. If A's number is 12, find the sum of A, B, and C.
甲数和乙数的比是3：5，乙数和丙数的比是4：7．若甲数是12，求甲，乙，丙三数的和．
<gadget id="calculator">5 / 3</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">12 * (5/3)</gadget>
<output>20</output>

<gadget id="calculator">7 / 4</gadget>
<output>7/4 = around 1.75</output>

<gadget id="calculator">12 * (5/3) * (7/4)</gadget>
<output>35</output>

<gadget id="calculator">12 + 20 + 35</gadget>
<output>67</output>

<result>67</result>