The two masters and apprentices can complete a project in 2 days, the apprentice can complete it in 6 days, and the master can complete it in how many days.
师徒二人合作2天可以完成一件工程，徒弟单独做需6天完成，师傅单独做需多少天完成．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/2) - (1/6)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3)</gadget>
<output>3</output>

<result>3</result>