For the three-part question that follows, provide your answer to each question in the given workspace. Identify each part with a coordinating response. Be sure to clearly label each part of your response as Part A, Part B, and Part C.

Use the information below for Part A, Part B, and Part C.
Simple interest varies jointly with principal and time. Tim deposited $1,500 into an account and left it for 6 years. He earned $450 interest.

Part A: Write the general formula. Be sure to define your variables.

Part B: Find the constant of variation and write the explicit formula.

Part C: How much interest would Tim have earned if he had deposited $4,500 into the account and left it for 12 years?

Show your work support your answer.