In ancient poetry, five-character quatrains are four-line poems, each with five characters; seven-character quatrains are four-line poems, each with seven characters. On the contrary, the number of words is 20 less, so how many five-character quatrains are there in this collection of poems?
古诗中，五言绝句是四句诗，每句五个字；七言绝句是四句诗，每句都是7个字，有一本诗集，其中五言绝句比七言绝句多13首，总字数反而却少了20个字，则这本诗集中五言绝句有多少首？
<gadget id="calculator">13 * 5 * 4</gadget>
<output>260</output>

<gadget id="calculator">260 + 20</gadget>
<output>280</output>

<gadget id="calculator">4 * 7</gadget>
<output>28</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">280 / 8</gadget>
<output>35</output>

<gadget id="calculator">35 + 13</gadget>
<output>48</output>

<result>48</result>