Let the numerator be x
numerator =x
denominator = x - 4
fraction =

Add 3 to numerator and denomiator
numerator = x + 3
denominator = x -4 + 3 = x - 1
fraction =

=

cross multiply:
2(x + 3) = 3(x - 1)
2x + 6 = 3x - 3
3x - 2x = 6 + 3
x = 9
Orignal fraction =

=

=

Sum of the numerator and denominator = 9 + 5 = 14