C is the correct answer. explain how? Thanks!

The following facts pertain to an Enterprise Fund of a city at its fiscal year-end: 1) Outstanding bonds issued to provide founding for capital projects $13,000,000 2) Customer service revenue for utility services provided this year $18, 500,000 3) Annual transfer to General Fund $750,000 4) Capital bond proceeds not yet spent for capital projects $7,000,000 5) Current year payroll expenditures $6,000,000 6) Interest earnings on investments $150,000 7) Fair market value of fixed assets donated by a contractor $4,000,000 8) Net book value of all remaining fund capital assets $2, 500,000 9) Outstanding bonds issued to pay for clean energy research $8,000,000 Based on this information, the total of this fund's Net Investment in Capital Assets is a. $0 b. $7, 500,000 c) $500,000 d) ($7, 500,000)