Xiao Ming's family is going on an outing with four other good friends' families, and they will bring some black tea drinks when they go. If they prepare 6 bottles for each family, they will need 30 bottles. When I arrived at the supermarket, I was catching up with two brands of black tea beverages for an event. The original price of the beverage was 4 yuan. A black tea was "buy five and get one free", and B black tea was sold at a 15% discount. Which kind of black tea did they choose? What is the difference? Yuan?
小明家人要和其他四个好朋友的家人一起去郊游，准备去时带一些红茶饮料，如果按每家6瓶准备，需要30瓶．到超市时正赶上两个品牌的红茶饮料搞活动，原价均是4元的饮料，A红茶"买五赠一"，B红茶打八五折销售，他们选择哪种红茶比较合适，相差多少元？
<gadget id="calculator">30 * 4 * 0.85</gadget>
<output>102</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<gadget id="calculator">5 * 4 * 5</gadget>
<output>100</output>

<gadget id="calculator">102 - 100</gadget>
<output>2</output>

<result>2</result>