Answer
$d=1.5$
$a_{n}=23.5+1.5n$
$ a_{5}=31;$
$a_{100}=173.5$
Work Step by Step
$d=a_{n+1}-a_{n}=26.5-25=28-26.5=29.5-28=1.5$
$a_{n}=a+\left( n-1\right) d\Rightarrow a_{1}=a+\left( 1-1\right) d=a=25$
$a_{n}=a+\left( n-1\right) d=25+\left( n-1\right) \times 1.5=25+1.5n-1.5=23.5+1.5n$
$a_{n}=23.5+1.5n\Rightarrow a_{5}=23.5+1.5\times 5=31;a_{100}=23.5+1.5\times 100=173.5$
