Answer
$a_{n}=-3n+10$
Or:
$a_{n}=7-3(n-1)$
Work Step by Step
We are given:
$7, 4, 1, -2$, ...
We see that the terms in the sequence go down by $3$ each time. In order to make the first term $7$, we add $10$:
$a_1=-3(1)+10$
$a_2=-3(2)+10$
$a_3=-3(3)+10$
$a_4=-3(4)+10$
...
$a_{n}=-3n+10$
Or:
$a_{n}=7-3(n-1)$