Liu Liang goes to school from home. When he leaves, he looks at the clock. If he walks 80 meters per minute, he will be 5 minutes late; if he rides a bicycle at 200 meters per minute, he can arrive at school 7 minutes earlier. How much time did Liu Liang have until class?
刘亮从家到学校上学，出发时他看看钟，如果每分钟步行80米，他将迟到5分钟；如果骑车每分钟行200米，他可以提前7分钟到校．刘亮出发时离上课有多少时间？
<gadget id="calculator">200 * 7</gadget>
<output>1_400</output>

<gadget id="calculator">80 * 5</gadget>
<output>400</output>

<gadget id="calculator">1_400 + 400</gadget>
<output>1_800</output>

<gadget id="calculator">200 - 80</gadget>
<output>120</output>

<gadget id="calculator">1_800 / 120</gadget>
<output>15</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<result>20</result>