One.
21
4
2 2 goes into any even number right away evenly. In this case though, the highest number would be 4.
1, 2, 4
2 goes evenly into 4 and 28
One.
The only number that goes into both 3 and 4 evenly is 1.
1, 2, 3, 4, 6, 12.
As 3 and 5 are Prime numbers, no other number will go evenly into them. (presuming that "evenly" means a multiple of two). If you are looking for a common factor of 3, 4, and 5, then the answer is 1.
136
21
4
The HCF is 4
2 2 goes into any even number right away evenly. In this case though, the highest number would be 4.
Just 1.
1, 2, 4.