So we got sales data for six months which has 4 different marketing type campaigns running. One of them is in-store which runs for 3 months only. Another campaign is social which has the least spend but runs for 6 months. Other 2 run for 2 & 3 months respectively. If you run linear regression it gives social campaign as significant. How I consider the time range of these campaigns and the spend for each towards my mix marketing model.

My question here is how do you come up with a mix marketing model which considers the factors such as the cost for each marketing campaign and the total time duration when it was run.