Tanya offered to sell her used iPhone9 to Omar for $100. Omar said he wanted to think about it, while he checked on the cost of replacing the battery for it, so he askedTanya if he could have a few weeks to think about it and Tanya said "sure." Three days later, after determining that it was a good deal, Omar returned to Tanya to accept the offer, and said "Hey- nice to see you. I want to tell what I decided." But before he could say anything else, she said,"By the way- I changed my mind- the price is now $200- do you still want the phone?" Omar replied "That's not fair. I accept the offer of $100, but not a penny more." Is there a valid contract at $100? Explain.