Xiao Ming's crayon used to be 9 cm long, but now there are 75 mm left. How much mm is used for this crayon?
小明的蜡笔原来长9厘米，现在还剩75毫米，这只蜡笔用去了多少毫米？
<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<gadget id="calculator">90 - 75</gadget>
<output>15</output>

<result>15</result>