The size of shoes is usually in "yard" or "centimeter", and the conversion relationship between them is: b=2a-10 (b indicates the number of yards, a indicates the number of centimeters). Mr. Zhang usually wears size 42 shoes. What is the actual length of the shoes he wears?
鞋的尺码通常用"码"或"厘米"作单位，它们之间的换算关系式：b=2a-10(b表示码数，a表示厘米数)．张老师一般穿42码的鞋，他穿的鞋实际长多少厘米．
<gadget id="calculator">42 + 10</gadget>
<output>52</output>

<gadget id="calculator">52 / 2</gadget>
<output>26</output>

<result>26</result>