a and b can do a piece of work in 7 days, b and c in 8 days, c and a in 9 days. how long will c take to do it? Choose the correct choice from the following choices.
A) 14.1 days	B) 18.8 days	C) 21.4 days	D) 24.3 days	E) 26.5 days
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 / 9</gadget>
<output>7/3 = around 2.333333</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<gadget id="calculator">21 / 8</gadget>
<output>21/8 = around 2.625</output>

<gadget id="calculator">3 + (21/8)</gadget>
<output>45/8 = around 5.625</output>

<gadget id="calculator">(7/3) + (45/8)</gadget>
<output>191/24 = around 7.958333</output>

<gadget id="calculator">(191/24) / 2</gadget>
<output>191/48 = around 3.979167</output>

<gadget id="calculator">(191/48) - 3</gadget>
<output>47/48 = around 0.979167</output>

<gadget id="calculator">21 / (47/48)</gadget>
<output>1_008/47 = around 21.446809</output>

<result>C</result>
a and b can do a piece of work in 7 days, b and c in 8 days, c and a in 9 days. how long will c take to do it?
divide(multiply(7, const_3), subtract(divide(add(divide(multiply(7, const_3), 9), add(divide(multiply(7, const_3), 7), divide(multiply(7, const_3), 8))), const_2), divide(multiply(7, const_3), 7)))
"2 c = 1 / 8 + 1 / 9 – 1 / 7 = 47 / 504 c = 47 / 1008 = > 1008 / 47 = 21.4 days the answer is c ."