K.
1.) 3, 6, 9, 12, 15, ...
The common difference is 3.
2.) 4, 8, 12, 16, 20, ...
The common difference is 4.
3.) 1, 3, 5, 7, 9, ...
The common difference is 2
4.) 1, 1/2, 1/4, 1/8, 1/16, ...
The common difference is -1/2
5.) 2x+1, 3x+3, 4x+5, 5x+7, ...
The common difference is x+2.
Hope it helps.
