The follow table shows total dollar sales (in thousands) for a local retailer for various years. Year 2020 2021 2022 2023 2024 Sales ($) 15 21 27 33 39 a) What was the the sales for 2020? $ b) By how much did sales increase by each year? $ c) Find a linear equation that models the data. Let x = = 1 correspond to 2020 and let S be in thousands. S= = x + d) Use your equation to predict sales in 2025. The projected sales amount in 2025 is $ ​