A and B each process the same number of parts, A makes 11 parts per hour, and B makes 7 parts per hour. The two started work at the same time, and A helped B to work for 4 hours after A completed the work. How many parts does B make?
甲、乙二人各自加工同样多的零件，甲每小时做11个，乙每小时做7个．二人同时开工，甲完工后又帮乙做4小时，乙才完工．问乙做的零件有多少个？
<gadget id="calculator">11 - 7</gadget>
<output>4</output>

<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">11 * 1</gadget>
<output>11</output>

<gadget id="calculator">11 - 4</gadget>
<output>7</output>

<result>7</result>