Teacher Wang bought a pair of table tennis rackets and 4 table tennis balls, which cost 68 yuan in total. A pair of table tennis rackets is 52 yuan, how much is a table tennis ball?
王老师买了一副乒乓球拍和4个乒乓球，一共用去68元．一副乒乓球拍52元，一个乒乓球多少元？
<gadget id="calculator">68 - 52</gadget>
<output>16</output>

<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<result>4</result>