The size of the shoe refers to the length of the sole, usually in "yard" or "centimeter", the relationship between them can be expressed by y=2x-10 (y represents the number of yards, x represents the number of centimeters). Fang Fei bought a new pair of sandals with a sole length of 20 cm. What is the size?
鞋的尺码是指鞋底的长度，通常用"码"或"厘米"作单位，它们之间的关系可以用y=2x-10来表示(y表示码数，x表示厘米数)．芳菲新买了一双凉鞋鞋底长20厘米，是多少码．
<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<result>30</result>