Answer
See below.
Work Step by Step
$a_1=5$
$a_2=a_1+5=5+5=10$
$a_3=a_2+5=10+5=15$
$a_4=a_3+5=15+5=20$
$a_5=a_4+5=20+5=25$
The first differences: $a_2-a_1=a_3-a_2=a_4-a_3=a_5-a_4=5$
The second differences: $5-5=5-5=5-5=0$.
The first differences are constant; thus it is linear.
