Xiaohua's wall clock is 4 minutes slower than the standard per hour. Xiaohua aligns the wall clock when he goes to school at 7:00 in the morning, and the wall clock points to exactly 9:00 when he goes to bed at night. Q: What is the standard time at this time?
小华家的挂钟比标准每小时慢4分钟，小华早上7时上学时把挂钟对准，晚上睡觉时挂钟正好指着9时．问：此时的标准时间是多少？
<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 - (1/15)</gadget>
<output>14/15 = around 0.933333</output>

<gadget id="calculator">14 / (14/15)</gadget>
<output>15</output>

<gadget id="calculator">7 + 15</gadget>
<output>22</output>

<gadget id="calculator">22 - 12</gadget>
<output>10</output>

<result>10</result>