Xiaoyu goes from home to school. If she walks 80 meters per minute, she can arrive at school 6 minutes before class starts. If she walks 50 meters per minute, she will be late for 3 minutes. How many minutes does Xiaoyu plan to arrive at school on time?
小羽从家去学校，如果每分钟走80米，能在上课前6分钟到校，如果每分钟走50米，就要迟到3分钟，小羽计划用多少分钟准时到学校？
<gadget id="calculator">50 * 3</gadget>
<output>150</output>

<gadget id="calculator">80 * 6</gadget>
<output>480</output>

<gadget id="calculator">150 + 480</gadget>
<output>630</output>

<gadget id="calculator">80 - 50</gadget>
<output>30</output>

<gadget id="calculator">630 / 30</gadget>
<output>21</output>

<result>21</result>