The average temperature of thefirst three days of a week is $$27^\circ$$ and of the next three days is $$29^\circ$$. If the average of the whole of the week is $$28.5^\circ$$ the temperature of the last day of the week is

A

$$31.5^\circ$$

B

$$10.5^\circ$$

C

$$21^\circ$$

D

none