Your friend Bob, is going through some tough time financially and you want to help him out. You are negotiating to lend a 7-year loan of $25,000 to him. To repay you, Bob will pay $2,500 at the end of Year 5, $5,000 at the end of Year 6, and $7,500 at the end of Year 7, plus a fixed but currently unspecified cash flow, X, at the end of Years 1 through 4. Because you and Bob are long-time friend, you are confident that Bob will make all 7 yearly payments. You regard 8% as an appropriate rate of return on this 7-year loans. What amount does Bob have to pay from Year 1 to Year 4 (i.e., what is X?). To clarify, the amount X is same from Year 1 to Year 4.

You must show all calculation steps, providing a final answer only will not get you full marks.