Xiao Ming's family was eating in a restaurant, and the waiter missed the decimal point of the menu price of a plate when paying the bill, and the result was an extra 256.5 yuan. If the unit price of the dishes in this restaurant is all with one decimal place, what should be the unit price of the dish that the waiter miscalculated?
小明一家在餐馆吃饭，结账时服务员把一盘菜单价的小数点看掉了，结果多算了256.5元．如果这家餐馆菜品的单价都是一位小数，那么服务员算错的那盘菜的单价应该是多少？
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">256.5 / 9</gadget>
<output>28.5</output>

<result>28.5</result>