Alt Inv: Real Estate DCF Model Question building, following, financing, office, investor

rosewhite

An investor made the following purchase:

Bought an office building for $500,000 using 90% financing.
The borrowing cost was 10%.
They received $29,000 at year-end from rentals.
They sold the building for $520,000 at the end of the year.

Assuming a flat tax rate on income and capital gains of 25% what was the return on equity?

A) +6%.
B) -3%.
C) +10%.

ATCF = (Income + Capital Gain - Interest)(1 - tax rate) - Principal component of Mortgage Amount.

From the data provided, there is no way to calculate the Principal component of Mortgage.
Is it OK to just ignore it and assume NOI = ATCF?