How many license plates are possible if they have:
a.) Three letters followed by three digits?
b.) Four letters followed by three digits?
with replacement
a) $$26^3*10^3$$
b) $$26^4*10^3$$
B.) Four letters followed by three digits
A. Without replacement, 26*25*24*10*9*8
B. Same situation, 26*25*24*23*10*9*8
+4473 
