1. The problem statement, all variables and given/known data Assuming that the average surface brightness within the effective radius is 19 mag/arcsec2, use the definition of the effective radius to estimate what the effective radius in kpc would be for NGC 4216 if it was an elliptical galaxy. 2. Relevant equations All the logs are base 10 log(i(r)/ie)= -3.3307 [(r/re)^1/4-1] 3. The attempt at a solution I am given ie in the problem which is 19. I tried to find i(r) using i(r)=apparent magnitude+2.5log(surface area) but that gives me a negative i(r) which does not make sense and gives me log of a negative value which does not exist. Can you tell me what I need to do, not necessarily the answer but values i could use or i need to find to get this. Thank you.