At 3 o'clock, the angle formed by the minute hand and the hour hand of the clock is 90°, what is the angle formed at 9 o'clock?
3时的时候，钟表的分针和时针形成的角是90°，9时的时候形成的角是多少．
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>