Answer:
$158.75, if the total balance is due at check out.
Step-by-step explanation:
Mr. Thomas owes $128.75 and has just increased this by $30 for today's visit. $128.75 (owed) plus $30 (today's visit) equals $158.75.
It may be that the company will allow Mr. Thomas to pay at least 50% ($79.38) or 30% ($52.92), and then pay the rest later.