A salesperson received a 6-percent commission on the amount of sales up to and including $10,000, and r-percent commission on the maont of total sales over $10,000. If the salesperson received a total commission of $920 on total sales of $14,000, what was the value of r?

A. 3.2
B. 4.3
C. 6.6
D. 8.0
E. 9.2