I have some given data, which result in a logrithmic trendline of

u = -28.593*ln(k) + 144.76

The object is to empirically define "c" and "j" in the following equation by back substitution:

u = c*ln(j/k) ; only valid where k approaches j

My thought is to set the equations equal to each other, but then I get stuck:

-28.593*ln(k) + 144.76 = c*ln(j/k)

Any ideas?