Answer
a) A codomain can be set of all 10-digit numbers (if phone numbers are 10 digit).
b) A codomain could be all natural numbers less than 100,000,000 (all natural numbers with 8 digits or less)
c) {A,B,C,D,E,F} could be a codomain.
d) A codomian could be all cities and towns that exists in the world.
Work Step by Step
a) A codomain can be set of all 10-digit numbers (if phone numbers are 10 digit).
With this codomain function is not onto because there will be 0-digit numbers that are assigned outside the class.
The function is onto only if we reduce this set to the 10-digit numbers of the phone of the students.
b) A codomain could be all natural numbers less than 100,000,000 (all natural numbers with 8 digits or less)
This function would not be onto as we do not have that many students in the class.
It would be onto only if we take the actual number of students taking the class.
c) {A,B,C,D,E,F} could be a codomain. It does not have to be onto as perhaps, none of the students scored an "A".
It would be onto if, for every grade, there is atleast one student who received that grade.
d) A codomian could be all cities and towns that exists in the world.
Since the class do not have that many students, the function would not be onto.
It becomes onto if we select only the towns and cities from which the students come from.
