Answer :
In order to get an 81 average,
the student has to get 81x5=405
71+96+90+73+?=405
330+?=405
405-330=75
he needs to get an 75
the student has to get 81x5=405
71+96+90+73+?=405
330+?=405
405-330=75
he needs to get an 75