Take the LCM of 3ab and 5/2b like in regular addition of fractions. So for that you will have to multiply 3ab with 2b which will give you 6ab^2.
Well what i meant is, that since you are not given the denominator for 3ab you can assume that it is a fraction with denominator 1, so that the lcm(1,2b)=2b.
Then you can simply multiply 3ab by 2b and 1 by 2b to get a common denominator for 3ab and 5 that is 2b.
So the answer will turn out to be (6ab^2 +5)/2b.
I believe that this is correct, but I could be wrong. Someone check my math and verify that it is correct. I don't want to give them the incorrect process. I cannot remember if you can get rid of the b on the bottom or not...