He did not determine his new balance correctly. His balance now is $-1,840
1) Gathering the data
$-1,280 negative balance
Kendall spent $560, so money out then: $-560
2) So Kendall did not determine correctly the new balance, since He was in debt, and has increased negatively
-1,280-560 =-1,840
3) So the answer is no, He did not determine his new balance correctly. His balance now is $-1,840