The sixth grade students made 176 butterfly specimens and displayed them on 13 exhibition boards. 8 pieces are attached to each small display board, and 20 pieces are attached to each large display board. So how many big display boards are there?
六年级同学制作了176件蝴蝶标本，分别在13块展板上展出．每块小展板贴8件，每块大展板贴20件．那么大展板有多少块．
<gadget id="calculator">176 - 104</gadget>
<output>72</output>

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">72 / 12</gadget>
<output>6</output>

<result>6</result>