Both Li Hong and Wang Fang want to buy the same book. Li Hong buys this book with a difference of 5.8 yuan, and Wang Fang buys this book with a difference of 7.2 yuan. When they buy this book together, there is still 2 yuan left. How much is the book.
李红和王芳两人都想买同一本书，李红买这本书差5.8元，王芳买这本书差7.2元，两人合起来买这本书还剩下2元，这本书多少元．
<gadget id="calculator">7.2 + 2</gadget>
<output>9.2</output>

<gadget id="calculator">5.8 + 2</gadget>
<output>7.8</output>

<gadget id="calculator">7.8 - 2</gadget>
<output>5.8</output>

<gadget id="calculator">9.2 + 5.8</gadget>
<output>15</output>

<result>15</result>