It takes 12 days for the master and apprentice to process a batch of parts. After 4 days of cooperation, the master alone takes 10 days to complete the rest. How many days will it take for the master to complete this work alone?
师徒二人加工一批零件，二人合作需12天完成，二人合作4天后，余下的由师父单独用10天完成，则师父单独完成这项工作需要多少天？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 4</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) / 10</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / (1/15)</gadget>
<output>15</output>

<result>15</result>