HOw can i do this

Question

1. The department of History has just bought a new photocopier. Any person using the photocopier must enter an identification code.  You have been asked to do the following: 

• Write a program that determines whether identification codes typed by users of a photocopier are valid, and prints appropriate messages. If the identification code, which is a four-digit number, is correct your program computes the cost of copying according to the table below.
• Your program should prompt the user for an identification code, read it and determine whether it is valid. An identification code is valid if its rightmost digit is correct.  A correct digit is equal to the remainder of the sum of the other three digits divided by 7. For example, a valid code that gives a correct digit is   7011.  However, 9999 is not a valid code. 7011 is a valid code because (7+0+1)%7 = 1, which is equal to the rightmost digit of 7011.  But 9999 is not a valid code because (9+9+9)%7 = 6, which is not equal to the rightmost digit of  9999.

Correct digits are assigned as follows:

Student: 1, 2   (means 1 or 2)

Teacher: 3, 4, 5

Secretary: 6

Others: 7, 8, 9

Number of pages	1 to 10	10 to 20	>20
Students	0.10 Dhs	20% off	40% off
Teachers	0.30 Dhs	30% off	40% off
Secretaries	0.20 Dhs	25% off	40% off
Others	0.60 Dhs	10% off	20% off