The school buys "Dictionary for Primary School Students", 4 of which are hardcover and 9 are paperback, for a total of 60.6 yuan. If you exchange 2 paperbacks with 1 hardcover, you will have to pay another 1 yuan. How much is each hardcover book.
学校买《小学生字典》，4本是精装本的，9本是平装本的，共用60.6元．如果用1本精装本调换2本平装本要再付1元．精装本每本多少元．
<gadget id="calculator">60.6 + 4</gadget>
<output>64.6</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 + 9</gadget>
<output>17</output>

<gadget id="calculator">64.6 / 17</gadget>
<output>3.8</output>

<gadget id="calculator">3.8 * 2</gadget>
<output>7.6</output>

<gadget id="calculator">7.6 - 1</gadget>
<output>6.6</output>

<result>6.6</result>