Marvin offers to sell his old computer to Harold for $800.00. Harold really wants to buy the computer, but he doesnt know if he can come up with the money.

Harold asks Marvin IF Marvin would give Harold 3 days to think about the offer and try to gather the money??

Marvin agrees, so long as Harold pays Marvin $100.00 to keep the offer open for 3 days.

Harold gives Marvin $100.00 to keep the offer open for 3 days.

Marvin keeps the offer open for 3 days.

What type of contract is this called, if any?