In a situation where the Engineer issues a Purchase Order $($PO$)$ under their letterhead, but they are not the Employer, what is the consequence of this mistake?

a$)$ The contract becomes voidable for misrepresentation.

b$)$ The mistake is not considered material, and the contract remains valid

c$)$ The contract is considered void from the beginning.

d$)$ The mistake only affects the reason for entering into the contract