A piece of chalk used to be 8 cm 6 mm long. Now this piece of chalk is 6 cm 8 mm long. How many mm has been used?
一支粉笔原来长8厘米6毫米，现在这支粉笔长6厘米8毫米，用去了多少毫米？
<gadget id="calculator">86 - 68</gadget>
<output>18</output>

<result>18</result>