The average of the three numbers of A, B, and C is 70, A: B = 2: 3, B: C = 4: 5, what is the number of B.
甲乙丙三个数的平均数是70，甲：乙=2：3，乙：丙=4：5，乙数多少．
<gadget id="calculator">70 * 3</gadget>
<output>210</output>

<gadget id="calculator">8 + 12 + 15</gadget>
<output>35</output>

<gadget id="calculator">12 / 35</gadget>
<output>12/35 = around 0.342857</output>

<gadget id="calculator">210 * (12/35)</gadget>
<output>72</output>

<result>72</result>