Answer:
C. was formed on January 18
Step-by-step explanation:
Since in the question it is mentioned that On Jan 8, Quastrar sent the letter for selling the restaurant supplies to Hylian company for $10,000. On Jan 17, Quastrar sent the revoking letter offer and the same would be received by Hylian on Jan 21. On Jan 18, Hylian mailed the letter regarding the acceptance to Quastrar and the same would be received by Quastrar on Jan 20.
So, the contract between them would be created on Jan 18 as the acceptance is sent on Jan 18 i.e. prior the revocation letter