lnc=blnr+lna

Find lna and b, and excel can calculate directly.

Matlab has been useless for n years.

polyfit(lnr，lnc， 1)

Your model is wrong. I'd rather choose the one that fits twice than yours. I don't know what your problem is. If modeling is involved, your data is too small, and if you collect the data yourself, then your data is even more problematic!