Question 55646
Ok, this is not thát hard:
We have to add 2 fractions with equal denominator (4ab). 
This means the solution will be of a type x/4ab. Let's add-up:
b + 3b = 4b, givin' us the 'x'-value.

We now have 4b/4ab. 

This we can simplify a bit more: 4b is present in the numerator ás in the denominator (4b/4ba) leaving us with the solution: 

1/a