Answer
The sequence is arithmetic.
Common difference $d=1.45$
Work Step by Step
We compute the difference between each term and the preceding term. If the difference is same, then the sequence is arithmetic.
$a_{2}-a_{1}=-8.6-(-10.05)=1.45$
$a_{3}-a_{2}=-7.15-(-8.6)=1.45$
$a_{4}-a_{3}=-5.7-(-7.15)=1.45$
$a_{5}-a_{4}=-4.25-(-5.7)=1.45$
$a_{6}-a_{5}=-2.8-(-4.25)=1.45$
The common difference $d=1.45$ is constant and therefore the sequence is arithmetic.