What is the angle between the minute hand and the hour hand at 21:30 on the clock face?
钟面上21点半时分针与时针的夹角是多少度．
<gadget id="calculator">3 * 30</gadget>
<output>90</output>

<gadget id="calculator">30 * 0.5</gadget>
<output>15</output>

<gadget id="calculator">90 + 15</gadget>
<output>105</output>

<result>105</result>