Answer
The sequence is arithmetic.
Common difference $d=-1.75$
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.
$a_{2}-a_{1}=18.25-20=-1.75$
$a_{3}-a_{2}=16.5-18.25=-1.75$
$a_{4}-a_{3}=14.75-16.5=-1.75$
$a_{5}-a_{4}=13-14.75=-1.75$
$a_{6}-a_{5}=11.25-13=-1.75$
The difference between each term and preceding term is constant and therefore the sequence is arithmetic.
Common difference $d=-1.75$
