skip 21.b
3.2 + 4d = 4
4d = .8
d = .2
Firt term is thus 3.2 - .2 = 3
an = 3 + .2(n-1)
= 2.8 + .2n
I think you can find the first 7 terms gieven the formula....
a100 = 2.8 + 20 = 22.8
+36915 
