Xiaohong buys 4 AA batteries and 3 pencils of 0.5 yuan, and the total cost is 9.9 yuan. How much is the price of each AA battery?
小红买4节五号电池和3枝0.5元的铅笔，一共用了9.9元，每节五号电池的价钱是多少元？
<gadget id="calculator">0.5 * 3</gadget>
<output>1.5</output>

<gadget id="calculator">9.9 - 1.5</gadget>
<output>8.4</output>

<gadget id="calculator">8.4 / 4</gadget>
<output>2.1</output>

<result>2.1</result>