If I take the ln of y= (ab)/(cd) is that going to be lna+lnblnc+lnd or lna+lnblnclnd?
...to put it simply, I'm asking if I should subtract the whole quantity of the divisor or just the first one?
...to put it simply, I'm asking if I should subtract the whole quantity of the divisor or just the first one?

Try splitting it into two steps. First, consider that
ln y = (ab)/(cd) = ln (ab)  ln (cd)
Then you know that
ln (ab) = ln (a) + ln (b)
and that
ln (cd) = ln (c) + ln (d)
So, now make the substitution in
ln (ab)  ln (cd) = [ln (a) + ln (b)]  [ln (c) + ln (d)]
Expand the negative into the brackets.
ln y = ln (a) + ln (b)  ln (c)  ln (d)
ln y = (ab)/(cd) = ln (ab)  ln (cd)
Then you know that
ln (ab) = ln (a) + ln (b)
and that
ln (cd) = ln (c) + ln (d)
So, now make the substitution in
ln (ab)  ln (cd) = [ln (a) + ln (b)]  [ln (c) + ln (d)]
Expand the negative into the brackets.
ln y = ln (a) + ln (b)  ln (c)  ln (d)