Answer
$a_{5}=1150$
Work Step by Step
$a_{n}=a+\left( n-1\right) d\Rightarrow a_{100}=a+\left( 100-1\right) \times \left( -20\right) =-750\Rightarrow a=99\times 20-750=1230$
$d=-20$
$a_{n}=a+\left( h-1\right) \times d\Rightarrow a_{5}=a+\left( 5-1\right) d=1230-80=1150$
