Adam is sitting with a group of his friends outside a public house in a harbour. He says that he will give $100 to anyone who can swim across the harbour. Adams puts that amount of money on the table to show the seriousness of his challenge. Ben is not with Adam's group but is sitting at a table next to Adam. He hears the promise but does not say anything. Suddenly a child falls into the water from the other side of the harbour. Ben dives into the water and begins to swim to her rescue. As Ben is approaching the child, Adam shouts out:

'Don't think you are going to get my $100, because I am withdrawing my offer.'

Ben nonetheless rescues the child and climbs out onto the other side of the harbour.

Explain, with reasons, whether Ben can claim $100 from Adam under the law of contract.