Roll Number. A particular institute assigns an 8-digit roll number to any enrolled student. The 8 digit roll number is divided into 2 sections: the first one consisting of three digits, out of which, the first two digits refer to the year in which the student has joined and last digit refers to the department in which the student has enrolled.

The second section consists of five digits, which refer to the serial number of the student. The institution has 6 departments, so the 3rd digit of the first section of the roll number can take values from 1 to 6. The last two digits for a year can take values from 0 to 9. Similarly the 5-digit serial number can takes values from 0 to 9.

a. How many possible serial numbers are there?

b. How many possible first three digits are there?

c. How many possible roll numbers are there?