Dr. Long adds 4 to the number on a card, multiplies it by 7, subtracts 3, and divides it by 5. The number obtained is 12. What is the number on this number card?
龙博士将一个卡片上的数加4，乘7，减3，再除以5，得到的数是12，这个数卡片上的数是多少．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">7 / 5</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">4 * (7/5)</gadget>
<output>28/5 = around 5.6</output>

<gadget id="calculator">12 - (28/5)</gadget>
<output>32/5 = around 6.4</output>

<gadget id="calculator">(3/5) + (32/5)</gadget>
<output>7</output>

<gadget id="calculator">7 / (7/5)</gadget>
<output>5</output>

<result>5</result>