Baxter, a plumber, wants to submit a bid on a city sewer project. He computes the cost, but mistakenly omits the cost of one item. Accordingly, he submits a bid of $$430,000$ to the city. The next highest bid is $$675,000,$ and

the rest of the bids are even higher. The city is happy to have such a low bid, so it accepts Baxter's bid and awards him the contract for the job, even though the city engineer is of the opinion the job cannot be done for less than

$$650,000.$ In this case:

a$.$ Baxter must perform for the agreed upon price, because he has made a unilateral mistake.

b$.$ the city was aware of Baxter's mistake. When it accepted the bid, with knowledge of Baxter's mistake, the city sought to take an unconscionable advantage of Baxter's error.

c$.$ there is a case of mutual mistake.

d$.$ All of these are correct.