An obligation of $2,500 falls due at the end of 7 years. If money is valued at r1/12 = 0.84% find the equivalent debt at the end of

(a) 3 years, ($1,673.26)

(b) 10 years. ($2,563.53)

I understand how to solve A and get the same answer, however, the solution for B according to it is 2500 x (1.0084)^3 and I don't understand why. In my view, it should be 2500 x (1.0084)^36. Could anyone help me clarifying why it works like this?