Final answer:
To find the greatest number, arrange the digits in descending order: 8, 8, 6, 4, 3, 2, 1. The greatest number using each digit once is 8864321.
Step-by-step explanation:
To find the greatest number that Tara can make using each digit once, we need to arrange the digits in descending order. The digits given are 4, 6, 8, 2, 8, 3, and 1. Ordering them in descending order, we get 8, 8, 6, 4, 3, 2, and 1. Therefore, the greatest number Tara can make using each digit once is 8864321.