How do i do this? i have to make same common denominator and answer in book is 2.

A/2+3/(a-3)=a/(a-3)  

You want to make the common denominator (2a-6) which is 2(a-3) then you will have:

(a/2)((a-3)/(a-3))+(3*2)/(2(a-3))=2a/(2(a-3))

(a^2-3a)/(2a-6)+6/(2a-6)=2a/(2a-6)  multiplying the equation by (2a-6) leaves

a^2-3a+6=2a

a^2-5a+6=0  now factor...

a^2-2a-3a+6=0

a(a-2)-3(a-2)=0

(a-3)(a-2)=0

So there are two solutions for the value of a:

a=2 and 3