Answer:
There are two unknow values, your 8% which is the decrease and the main value which is "the sales last year".
It is correct, the number you gave as an answer $9798,91. Let's get the explanation by a rule of three.
Explanation:
The 100 % was "the sales last year", the 8% are what the sales decreased but you don't have that number, you have the result in the substraction, $9015. So this are the step by step, hope you understand!