Feifei played the piano during the summer vacation, from July 10 to August 15, 4 hours a day. How many hours did he play during this time?
菲菲暑假弹钢琴，从7月10日开始到8月15日，每天要弹4小时．这段时间他一共弹了多少小时？
<gadget id="calculator">31 - 10</gadget>
<output>21</output>

<gadget id="calculator">21 + 1 + 15</gadget>
<output>37</output>

<gadget id="calculator">4 * 37</gadget>
<output>148</output>

<result>148</result>