If Mark's property has $850,603 in gross potential income and $72,000 in vacancy loss, what is the NOI after accounting for $45,018 in operating expenses?

To determine the Net Operating Income (NOI), you start with the gross potential income and subtract both the vacancy loss and the operating expenses.

First, calculate the effective gross income by subtracting the vacancy loss from the gross potential income:

[ \text{Effective Gross Income} = \text{Gross Potential Income} - \text{Vacancy Loss} ]

[ \text{Effective Gross Income} = 850,603 - 72,000 = 778,603 ]

Next, subtract the operating expenses from the effective gross income to arrive at the NOI:

[ \text{NOI} = \text{Effective Gross Income} - \text{Operating Expenses} ]

[ \text{NOI} = 778,603 - 45,018 = 733,585 ]

Thus, the correct answer is 733,585. This calculation shows how effective gross income and operating expenses interact to derive the NOI, which is a crucial metric for assessing the performance of an investment property. The answer reflects the appropriate financial assessment involving income generated from renting out the property after accounting for expected losses due to vacancies and necessary expenses incurred in managing the property.