Combining Data From Two Tables

Hello all - I'm relatively new to SQL and has been struggling with the below query. Any help is greatly appreciated. Thanks.

I have the following 2 tables:


I'm trying to get the below output:


Here's the SQL I've been using:
SELECT
a.PERSON_ID,
sum(a.AMOUNT),
CASE
WHEN b.JOB_CODE = 10 then "Level 2 Seller"
WHEN b.JOB_CODE = 15 then "Level 3 Seller"
ELSE
'Level 1 Seller'
END as "Job_Code"
FROM
tbl_SALES a,
tbl_JOBFUNCTION b
WHERE
a.PERSON_ID = b.PERSON_ID
GROUP BY
a.PERSON_ID,
b.JOB_CODE

Here's what my results are with the query I've been using:


Each person could have many job codes, but when they have 10 then they're consider "level 2".
- If they have 15 then they're "level 3".
- If they don't have either 10 or 15 then they're "level 1".
- If they have both 10 and 15 they're still "level 3".

Please help.

Thanks,
Jim