Teacher Wang bought three reference books. The "Mathematics Teaching Guide" is 12.5 yuan, the "Mathematics Handbook" is 2.9 yuan cheaper than the "Mathematics Teaching Guide", and the "Mathematics Exercise Volume" is 3.4 yuan more expensive than the "Mathematics Handbook". How much should I pay for "Mathematics Practice Paper"?
王老师买了三本参考书．《数学教学指导》12.5元，《数学手册》比《数学教学指导》便宜2.9元，《数学练习卷》比《数学手册》贵3.4元．《数学练习卷》应付多少钱？
<gadget id="calculator">12.5 - 2.9</gadget>
<output>9.6</output>

<gadget id="calculator">9.6 + 3.4</gadget>
<output>13</output>

<result>13</result>