Toughones, a car part manufacturer, entered into a contract to license computer

Toughones, a car part manufacturer, entered into a contract to license computer software from a Vizera Inc. for $250,000. This software is to be used to keep track of inventory, accounts receivable, and other financial data. After the software was installed, the computer system worked but it had a few glitches. Toughones refused to pay the full amount in the contract. To settle the dispute, the parties agree that $180,000 is to be paid as full and final payment for the software. Toughones paid the $180,000 as agreed. What kind of agreement did Toughones and Vizera reach in the end?
A) accord and satisfaction
B) preexisting duty
C) counteroffer
D) mirror image acceptance

This is for my business law class, anything will help