How do I calculate a Return on Investment (ROI) on Marketing Strategy?

I am writing a paper on a market plan for a product but I am stuck on the marketing budget and how and when the company should expect to make money based on the strategy chosen. Is there a formula for this? The fictional product is a new mobile phone selling nation wide. Any help will be appreciated. Thanks.

how much you need to spend to generate revenue. calculate revenue with profits after paying employee’s or yourself or any other costs included. that will be your ROI on investment.