Choice of Two Options for Paying off a Loan

"You can pay off a loan by paying the entire amount of £10,000 now or you can pay £5,000 now and £5,000 at the end of five years. Which is preferable when the nominal continuously compounded interest rate is:

a. 2.5%

b. 5%

c. 7.5%"

I thought this was a cash flow problem when I first looked at it but after going to the library and trying to read some finance books I have confused myself and think I am wrong and am not sure where to start. Is there anyone who can help me with part a (I will be able to do parts b and c if i can do part a!)?