Answer:
We have only 3 B available, and as per the requirement. we need to provide each of them with 1st preference. However, five students have the first preference as B, and we have only 3 B available. Thus, the dream of providing each of them with first preference job seems to be impossible, as we are 2 short of what is required, and that is 5. No combination is possible hence.
Explanation:
Remember we have 9 students, but we have only 3 B available and we have five students with B as first preference. Hence, we are 2 less than the number of B required. No way hence we can provide all the students the job, which is their first preference.