I am double-checking my answers because present and future values make me VERY nervous and I can't afford to mess up this grade!

On January 1, 2006 XYZ Co completed the following transactions (using 8% interest rate)

a)borrowed $10,0000 for 10 years. Will pay $8,000 interest at end of each year and repay $10,000 at end of tenth year.

Determine present value of debt.

I have 100,000*.4632=$46,320

(10 year period, 8% using present value of $1)

b)Established a plant addition fund of $400,000 to be available at end of year 5. A single sum that will grow to $400,000 will be deposited on January 1, 2006.

What is the single sum? What is total amount of interest revenue that'll be earned?

I have 400,000*.6806=$272,240as the single sum.

I have interest as 8% of 272,240=$21,779

c)Agreed to pay severance to discharged employee. Will pay $50,000 at end of first year, $75,000 at end of second year and $100,000 at end of third year.

Determine persent value of obligation.

I have:

50,000*.9259=46295

75,000*.8573=64297.5

100,000*.7938=79380

46925+64297.5+79380=$189,972.5

d)Purchase a $180,000 machine Jan. 1, 2006 and paid cash $60,000. Four-year note payable signed for the balance. Note will be paid in 4 equal year-end payments starting Dec 31, 2006.

What is amount of each of the equal annual payments? What is total amount of interest expense incurred?

I have:

180,000-60,000=120,000*3.3121=397,452/4=$99,363 is equal payments

120,000*8%=9600 int exp year one

(120,000-89763)*8%=2419 int exp year two

(120,000-89763-96944)*8%=

And this is where I run into a problem. Since it can't be negative, I assume I got the payments wrong? Anyone willing to knock some numbers around and help me see my mistake?