Answer
$d=12$
$a_{n}=\left( -1\right) +\left( n-1\right) \times 12$
$a_{5}=47;$
$a_{100}=1187$
Work Step by Step
$d=a_{n+1}-a_{n}=11-\left( -1\right) =23-11=35-23=12$
$a_{n}=a+\left( n-1\right) d\Rightarrow a_{1}=a+\left( 1-1\right) d=a=-1$
$a_{n}=a+\left( n-1\right) d=\left( -1\right) +\left( n-1\right) \times 12$
$a_{5}=\left( -1\right) +\left( 5-1\right) \times 12=47;a_{100}=\left( -1\right) +\left( 100-1\right) \times 12=1187$
