A and B have to process 770 parts. A processes 50 parts per hour, and B processes 40 parts per hour. A has processed for 1 hour before B joins in. How many hours does A process when the work is completed?
甲、乙两人要加工770零件，甲每小时加工50个，乙每小时加工40个，甲先加工了1小时乙才参加进来，完工时甲加工了几小时？
<gadget id="calculator">770 - 50</gadget>
<output>720</output>

<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<gadget id="calculator">720 / 90</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>