Question

a8=126, a10=146.
a1-? d-? a9-?

Answer 1

a8=a1+7d
a10=a1+9d

a10-a8=9d-7d
a10-a8=2d

2d=146-126=20
d=10

a8=a1+7*10
126=a1+70
a1=126-70
a1=56

a9=a8+d
a9=146+10
a9=156