Question 6 (2 points) How many different ways can we use six colors C = {C1, C2, C3, C4, C5, C6} to paint six balls B = {b1, b2, b3, b4, b5, b6}, each ball is painted by one color, such that ball b3 is not painted by color C1 and ball b1 is not painted by color C3?
a) 396
b) 480
c) 640
d) 720
e) 504
f) 576