describe how each sequence is generated and write down the next two terms:

a) 40 41 43 46 50 55
b)90 89 87 84 80 75
c)1 3 7 13 21 31
d) 2 6 12 20 30 42

PLEASE HELP its urgent!

Even I can see what's happening with the first one:

add 1, then add 2, then add 3, then add 4, etc.

Turn your imagination loose and see what you find. These are not difficult.