tryotherone: if you really have all the other letters then you know 25ac and 13dn and 20ac and 24ac. This narrows 18dn since you know the 2nd and 3rd digit for sure and know that the 1st digit is one of two possibilities. This means k^2 is one of two values, only one of which is a perfect square. This gives you k. That gives you two possibilities for K, only one of which is compatible with 12ac.
Or you can start with 12ac since you know the 1st and 3rd digit. Since you now it is > 17dn, you can infer there are only two integral values for K = (12ac - D)/R and then deduce k.