After adding a certain number to the numerator and denominator of the fraction \(1991/1994), the new fraction obtained is \(1996/1997), then what is the added number.
分数\(1991/1994)的分子、分母同加上某数后，所得的新分数是\(1996/1997)，则加上的这个数是多少．
<gadget id="calculator">1_994 * 1_996</gadget>
<output>3_980_024</output>

<gadget id="calculator">1_991 * 1_997</gadget>
<output>3_976_027</output>

<gadget id="calculator">3_980_024 - 3_976_027</gadget>
<output>3_997</output>

<gadget id="calculator">1_997 - 1_996</gadget>
<output>1</output>

<gadget id="calculator">3_997 / 1</gadget>
<output>3_997</output>

<result>3_997</result>