The problem doesn't state the compounding period?
If it is daily compounding, the daily interest rate = .06/365 = .00016438
So, n = 365 and in this case the number of years (t) = 290/365 = .79452
If S = total money to be paid back and So = money borrowed, then
S =So(1 + I/n)(nt) = $6100(1.00016438)(365*.79452) = $6397.81
If the calculation is done on a yearly basis, then S = So(1.06)(.79452) = $6389.04 I'd choose D !