It's kinda hard if you don't give the passage and/or actual question as well. But if my memory serves, look at table of elution volume vs. diameter. From that, you know you want an elution volume <10 mL by extrapolation. Then, look at the fluorescence vs. elution volume graph. To get smaller elution volumes, you use higher concentrations. So to get an elution volume <10 mL, you need a concentration >0.20 mM.