market mix modelling - sales peel off and optimisation

Hey there i have a fmcg client who wants to understand the impact of baseline sales and incremental sales, then whcih marketing tactis is contributing how much to the sales, ROIs, ideal level of spends, sales forecasting, spends reallocation and optimisation strategy.
Its for a soap category, please respond only you have prior experience working with marketing effectiveness, market mix modelling, mroi etc