Question 35843
a(7)=a(1)+6d = 40
a(22)=a(1)+21d=-100

Subtract the 1st from the 2nd to get:
15d=-140
d=-28/3

Now solve for a(1) in the 1st:
a(1)+6(-28/3)=40
a(1)-56=40
a(1)=96

Cheers,
Stan H.