Let Anupa's favorite fraction be .
Since it is equivalent to , clearly x < y.
It is give that the sum of the numerator and the denominator is $120$.
Therefore, x + y = 120 --- (1)
We need to find y - x.
Now, from (1),
y = 120 - x
So,
5x = 3(120 - x)
= 360 - 3x
5x + 3x = 360
8x = 360
x = 360/8
= 45
y = 120 - 45 = 75
y - x = 75 - 45 = 30
Hence, the difference between the denominator and numerator of Anupa's favorite fraction is 30.