Using the digits 4, 3, 5, form the greatest and smallest 3-digit numbers.

Here are the greatest and smallest 3-digit numbers for each set of digits:

a) Digits: 4, 3, 5
To form the greatest number, arrange the digits in descending order: 5, 4, 3.
To form the smallest number, arrange the digits in ascending order: 3, 4, 5.
Greatest number: $\boxed{543}$
Smallest number: $\boxed{345}$

b) Digits: 6, 1, 2
To form the greatest number, arrange the digits in descending order: 6, 2, 1.
To form the smallest number, arrange the digits in ascending order: 1, 2, 6.
Greatest number: $\boxed{621}$
Smallest number: $\boxed{126}$

c) Digits: 9, 7, 4
To form the greatest number, arrange the digits in descending order: 9, 7, 4.
To form the smallest number, arrange the digits in ascending order: 4, 7, 9.
Greatest number: $\boxed{974}$
Smallest number: $\boxed{479}$

d) Digits: 4, 5, 3
To form the greatest number, arrange the digits in descending order: 5, 4, 3.
To form the smallest number, arrange the digits in ascending order: 3, 4, 5.
Greatest number: $\boxed{543}$
Smallest number: $\boxed{345}$

e) Digits: 8, 7, 6
To form the greatest number, arrange the digits in descending order: 8, 7, 6.
To form the smallest number, arrange the digits in ascending order: 6, 7, 8.
Greatest number: $\boxed{876}$
Smallest number: $\boxed{678}$