Answer
$d=-18$
$a_{n}=47-18n$
$ a_{5}=-43;$
$a_{100}=-1753$
Work Step by Step
$d=a_{n+1}-a_{n}=11-29=-7-11=-25-\left( -7\right) =-18$
$a_{n}=a+\left( n-1\right) d\Rightarrow a_{1}=a+\left( 1-1\right) d=a=29$
So the nth term
$a_{n}=a+\left( n-1\right) d=29+\left( n-1\right) \times \left( -18\right) =29-18n+18=47-18n$
$a_{n}=47-18n\Rightarrow a_{5}=47-18\times 5=-43;a_{100}=47-18\times 100=-1753$
