Robert had a tax liability of $6,943 last year. In addition, he owed other taxes of $509. He was entitled to tax credits of $642 and withholding amounted to $610 per month. Calculate the amount of the refund or the amount of additional taxes due (as the case may be).

a) $510 Due

b) $510 Refund

c) $377 Due

d) $377 Refund