Answer
The answer is $A_{n}=-3n+10$.
Work Step by Step
The sequence must be arithmetic because a common difference of $-3$ is maintained. Thus the equation must be in form
$A_{n}=A_1+(n-1)d$
$=7+(n-1)(-3)$
$=-3n+10$.
Thus the answer is $A_{n}=-3n+10$.
