When it is necessary to inform a customer about a delay in their order, the proper communication format should be a .

Business letter

Explanation:

A BUSINESS LETTER is type of letter which a company or an organization can use to communicate with their client or with other company or organization and the main aim or purpose of a BUSINESS LETTER include the following; It help to inform a customer or a client about an order , it can be use to make inquiring and it can be use to help inform a customer or client concerning the delay in the order the Customer made from the company or the reason why the order was delay among others, which is why BUSINESS LETTER is of paramount or important it enables a company or organization to pass information to their clients or to another company.

Therefore the proper communication format a commpany or an organization can use to inform a customer about a delay in their order should be a BUSINESS LETTER.

answerall of these;

answerup to (3) three years;