A, B, and C three aircraft models stay in the air for: A's (2/3) is B's (4/7), B's (2/3) is C's (4/7), C's The time spent in the air was 13 minutes longer than that of A. Ask: How long did B stay in the air?
A，B，C三架飞机模型在空中停留的时间为：A的(2/3)是B的(4/7)，B的(2/3)又是C的(4/7)，C在空中停留的时间比A多13分钟，问：B在空中停留了多长时间？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">(2/3) / (4/7)</gadget>
<output>7/6 = around 1.166667</output>

<gadget id="calculator">(4/7) / (2/3)</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">(7/6) - (6/7)</gadget>
<output>13/42 = around 0.309524</output>

<gadget id="calculator">13 / (13/42)</gadget>
<output>42</output>

<result>42</result>