Question is asking about last ball that means balls are placed one by one, we are considering the event that the last ball (6th) will be placed in basket 3 that means first 5 balls can be placed at any of the 9 place (10-1) since one place (i,e, third basket) is to be reserved for 6th ball. and 6th ball is placed at only 3rd basket out of the rest of the five places.

The total number of ways doing this=COMBIN(9,5)*1=126

Total number of ways plaing 6 balls in 10 baskets=COMBIN(10,6)=210

Henec, the number of ways 6th ball can be place in 3rd basket=1

 Probability that the last ball will be placed in basket 3

=Favourable number of cases for placing 6th ball in 3rd basket/Total otal number of ways 6 balls can be placed in 10 baskets

=126/210

=0.6