Xiaoya's mother bought several bottles of yogurt with a unit price of 6.9 yuan for 50 yuan, and bought a pack of chocolates for 12.8 yuan, and got back 2.7 yuan. How many bottles of yogurt did mother buy? (solution by equation)
小亚的妈妈用50元买了几瓶单价为6.9元酸奶，又买了12.8元一包的巧克力，找回2.7元，妈妈买了几瓶酸奶？(用方程解)
<gadget id="calculator">50 - 2.7</gadget>
<output>47.3</output>

<gadget id="calculator">47.3 - 12.8</gadget>
<output>34.5</output>

<gadget id="calculator">34.5 / 6.9</gadget>
<output>5</output>

<result>5</result>