a tank is filled by 3 pipes a, b, c in 7 hours. pipe c is twice as fast as b and b is twice as fast as a. how much will pipe a alone take to fill the tank?	Choose the correct choice from the following choices
A) 25 hr B) 35 hr C) 40 hr D) 49 hr E) 50 hr
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<result>D</result>
a tank is filled by 3 pipes a, b, c in 7 hours. pipe c is twice as fast as b and b is twice as fast as a. how much will pipe a alone take to fill the tank?
multiply(add(add(multiply(const_2, const_2), const_2), const_1), 7)
"suppose pipe a alone take x hours to fill the tank then pipe b and c will take x / 2 and x / 4 hours respectively to fill the tank . 1 / x + 2 / x + 4 / x = 1 / 7 7 / x = 1 / 7 x = 49 hours answer is d"