88888
888...
The greatest 4-digit number with no repeated digits is... 9876
To be an even number then the final digit = 2. The largest single prime digit is 7 (as both 8 and 9 are composite). The greatest even number fulfilling the conditions is 77777772.
987,654
98,764
98,764
24
98
997
0
None, because you do not have three even digits. None, because you do not have three even digits. None, because you do not have three even digits. None, because you do not have three even digits.
Assign the digits from left to right, using the largest possible digit in each case. Don't forget to reserve an even digit for the last position.
It is 9998, or if the digits can't be repeated, it is 9876.