Mr. Zhang has two 50-cent stamps and two 80-cent stamps. How much denomination postage can he pay with these stamps?
张老师有50分和80分的邮票各两枚，他用这些邮票能付多少种面值的邮资？
<gadget id="calculator">6 + 2</gadget>
<output>8</output>

<result>8</result>