Playing in the playground, each person pays 15 yuan for the first hour, and 8 yuan for each hour thereafter. Junjun and his younger brother paid a total of 78 yuan after playing. How many hours did they play in the playground?
游乐场游玩，每人第一个小时付款15元，以后每小时付款8元，军军和弟弟游玩后共付了78元，他们在游乐场玩了多少个小时．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">78 - 30</gadget>
<output>48</output>

<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">48 / 16</gadget>
<output>3</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>