The hour hand on the clock goes from a number to an adjacent number, that is, it rotates 30 degrees around the center point, and how many degrees does the hour hand rotate around the center point from "12" to "3".
钟表上时针从一个数字走到相邻的一个数字，就是绕中心点旋转了30度，当时针从"12"绕中心点旋转多少度时到"3"．
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>