A laboratory analyst titrates a wastewater sample for alkalinity using 0.0200 N sulfuric acid and a phenolphthalein endpoint followed by a methyl orange (bromcresol green–methyl red) endpoint to pH 4.5. The sample volume is 100 mL and the burette readings are 4.80 mL to the phenolphthalein endpoint and 18.60 mL to the total endpoint. What is the total alkalinity of the sample expressed as mg/L as CaCO3?