y=mlog(x+a)+b; asymptote at x=5 implies that (x+a)=0 when x=5 so a=-5. When x=6, y=0, so 0=mlog(6-5)+b, and b=0, because log(1)=0. y=mlog(x-5), where m<>0 (m is not zero). This can also be written x=5+e^(y/m) or x=5+p^(y/m) if p is the logarithmic base if p<>e.