Ballpoint pens sell for 5.1 yuan in packages of 5 pieces, 7.2 yuan in packages of 8 pieces, and 1.2 yuan to buy one. There are 55 children in the class taught by Mr. Zhang, and Mr. Zhang will give each child a pen. So how much does Mr. Zhang cost at least?
圆珠笔5支包装售5.1元，8支包装售7.2元，买一支要1.2元．张老师教的班有55位小朋友，张老师要给每位小朋友1支笔．那么张老师至少要花多少钱？
<gadget id="calculator">7.2 * 7</gadget>
<output>50.4</output>

<result>50.4</result>