Okay so will have x be the denominator.
Numerator: 4x
Fraction:

which would be equivalent to 4.
If you add 10 to both the numerator and denominator the resulting fraction is

We multiply both sides of the equal side sign times (x + 10) we get...
4x + 10 = 2 * (x + 10)
4x + 10 = 2x + 20
4x - 2x = 20 - 10
2x = 10
x = 5 < denominator
4x = 4 * 5 = 10 < So the fraction is 10/5