License plates in india begin with a code that identifies the state and district where the vehicle is registered, and this code is followed by a four-digit identification number. these identification numbers are given sequentially, starting with , 0001, 0002, etc. once this sequence reaches , a letter from the set (a, z) is added (in order), and once these run out, additional letters are added, and so on. so the sequence of identification numbers proceeds as follows: , 0001,, , a, a0001, a, b, b0001, b,, z, z0001,, z, aa, aa0001, .. how many identification numbers are there using three or fewer letters? (b) if a district registers 200 million cars, how many identification numbers must have four letters?