During the Children's Day on June 1st, my father and mother took the army to the park, and bought tickets for a total of 10.5 yuan. It is known that the price of an adult ticket is equal to the price of two children's tickets, so how much is an adult ticket?
"六一"儿童节时，爸爸、妈妈带军军游公园，买门票共用了10.5元．已知一张大人票的价钱与两张儿童票的价钱相等，那么一张大人票多少钱？
<gadget id="calculator">1 + 2 + 2</gadget>
<output>5</output>

<gadget id="calculator">10.5 / 5</gadget>
<output>2.1</output>

<gadget id="calculator">2.1 * 2</gadget>
<output>4.2</output>

<result>4.2</result>