Answer:
Alpha is liable for nothing.
Step-by-step explanation:
Builders requested Alpha to make a discount (which is considered a counteroffer) but Alpha rejected it. At this point there was no valid offer anymore, and luckily for Builders, they lost the bid. Since a counteroffer invalidates an original offer, Alpha didn't have any type of obligation with Builders to perform at $75,000. The new price between them was $90,000, take it or leave it. Builder's president made a mistake when he made his counteroffer and if they had won the contract, then they would have needed to look at the other offers.