A bottle of milk is 3 yuan, and there are 15 bottles in a box of milk. How much does it cost to buy two boxes of milk like this?
一瓶牛奶3元，一箱牛奶有15瓶，买这样两箱牛奶需多少元钱．
<gadget id="calculator">3 * 15 * 2</gadget>
<output>90</output>

<result>90</result>