There are a number of cards, and each card has a number written on it, which is a multiple of 3 or a multiple of 4. Among them, the cards marked with multiples of 3 account for (2/3), and the cards marked with multiples of 4 account for (3/4 ), there are 15 cards marked with multiples of 12, so how many cards are there in total?
有若干卡片，每张卡片上写着一个数字，它是3的倍数或4的倍数，其中标有3的倍数的卡片占(2/3)，标有4的倍数的卡片占(3/4)，标有12的倍数的卡片有15张，那么，这些卡片一共有多少张．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(3/4) - 1</gadget>
<output>-1/4 = around -0.25</output>

<gadget id="calculator">(2/3) + (-1/4)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">15 / (5/12)</gadget>
<output>36</output>

<result>36</result>