Xiaohong, Xiaohong's mother, Xiaoming, and Xiaoming's mother played together in the park. They bought four tickets and spent a total of 110 yuan. Adult tickets cost 40 yuan each, and how much do children's tickets cost? (Solving problems with equations)
小红、小红的妈妈、小明、小明的妈妈四个人一块公园玩，买了四张门票共花了110元，成人票每张40元，儿童票每张多少钱？(用方程解题)
<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">110 - 80</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>