Answer: D. Enforce the contract.
Step-by-step explanation:
This falls under the doctrine of Promissory estoppel. This posits that when a party to a contract has invested their money into procuring the necessary tools to fulfil their part of the contract, the other party may not cancel the contract unless they pay the former party what they would have made from the contract.
This is because the party that used their money to procure tools (Susan in this case) would not have done so if the other party (Andy) had not made a promise to them in the contract that they would fulfil their part of the bargain.
The Courts would therefore enforce the contract.