Answer
$157$
Work Step by Step
We know that $a_n=a_1+(n-1)d.$
where $d$=common difference and $a_1$= the first term
Here $a_1=-1$ and $d=a_2-a_1=1-(-1)=2$
Hence, here we have
$a_n=-1+(n-1)\cdot2.$
Therefore $a_{80}=-1+(80-1)\cdot2\\=157.$