job needs to be done by 2 fitters and 2 electricians. There are 3 fitters, 3 electricians, and 1 fitter and electrician. How many ways are there to choose 4 people from 7 people to complete the task?
某件工作需要钳工2人和电工2人共同完成．现有钳工3人、电工3人，另有1人钳工、电工都会．从7人中挑选4人完成这项工作，共有多少种方法．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">18 - 9</gadget>
<output>9</output>

<gadget id="calculator">18 + 9</gadget>
<output>27</output>

<result>27</result>