a3=-23, a8=-8, d-?, a1-?

a3=a1+2d => a1+2d=-23

a8=a1+7d => a1+7d=-8

2d-7d=-23+8

-5d=-25

d=25/5

d=5

an=a1+(n-1)*d

-23=a1+(3-1)*5

-23=a1+10

-a1=10+23

a1=-33