Final answer:
b. Dispatched by Great Foundries
The acceptance of a contract offer by Great Foundries is effective when it is dispatched, according to the mailbox rule in contract law.
Step-by-step explanation:
The question is addressing the rules related to contract formation, specifically when an acceptance of an offer becomes effective. Under the mailbox rule, which is a common rule in contract law, an acceptance is generally effective upon dispatch if the parties have not agreed otherwise and the acceptance is transmitted in a manner expressly or impliedly authorized by the offeror. Therefore, the acceptance by Great Foundries is effective when it is: b. Dispatched by Great Foundries. This rule encourages prompt acceptance by assuring the offeree that the offer will not be revoked once the acceptance is dispatched, thereby creating a binding contract.