I am not sure as to what are you trying to do. I can also say that by having a = 6, b= 8, c =10 and d = 12 the equation is still satisfied. so pl tell us what exactly do you want to do or find out.
Edit: Also, please use parenthesis when necessary. What you wrote was
which is not what you wanted to say. You needed to write this as
(a + b x)/(c + d x)