Just choose a satisfying denominator, ( if the whole number is positive, then choose a positive denominator of course) the numerator will be equal to the denominator multiplied by the whole number.
5= 7( the denominator I chose) 7 x 5 = 35 then,
5 = 35 / 7
( if you understand what I mean)
Multiply the whole number by the denominator and you will get the numerator