The size of shoes is usually in "yard" or "centimeter", and the conversion relationship between them is: a=(1/2)b+5 (a represents the number of centimeters, b represents the number of yards). According to this relationship, if the size of the shoe is 20 cm, then what is the size of the shoe.
鞋的大小通常用"码"或"厘米"作单位，它们之间的换算关系是：a=(1/2)b+5(a表示厘米数，b表示码数)．根据这个关系，如果鞋子的大小是20厘米，那么鞋子是多少码．
<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">15 / (1/2)</gadget>
<output>30</output>

<result>30</result>