Answer & Explanation:
a). The contract between Lisa and Bob is valid and enforceable as a valid contract is an agreement between parties lacking no element. The contract was very detailed and well discussed regardless of Bob drinking it is still enforceable unless Bob can proof that the intoxication impaired his judgement and made him incompetent to sign the contract thereby making it void.
b). The contract will be valid if Bob signed it before the drinks arrived as the document was complete and his signature show acceptance of the terms of the contract.
c). A minor can not enter into a contract as they may lack the capacity to enter into a valid contract. As such, if Bob was a minor regardless of him being sober any contract signed by him can be completely voidable.