Teacher Wang bought two reference books. "Primary Mathematics Teaching Guidance" is 12.3 yuan, and "Mathematics Handbook" is 4.2 yuan more than "Primary Mathematics Teaching Guidance". How much does Mr. Wang pay?
王老师买了两本参考书．《小学数学教学指导》12.3元，《数学手册》比《小学数学教学指导》多4.2元．王老师应付多少钱？
<gadget id="calculator">12.3 + 4.2</gadget>
<output>16.5</output>

<gadget id="calculator">12.3 + 16.5</gadget>
<output>28.8</output>

<result>28.8</result>