Using Regression to Determine the Impact of Media Placements on Net Sales

A client wants to launch an ad campaign. He has already made a similar campaign in the past and now wants to leverage historical data to assess the impact of  his ads before making new investments.

What data are going to use?

A spreadsheet with 21 rows and the ff. columns for our purpose:

1. Broadcast - number of placements in broadcast media
2. Out-of-Home - number of out-of-home ads
3. Print - number of ads in print
4. Net.Sales - net of sales 

Here's how it looks:

Short Answer:

I already ran a regression analysis on Tableau and found that broadcast has the most impact on net sales. 
Coeff: (Intercept) - 133108.8 Broadcast - 12141.9 P-value - 1.95e-10 Adj. R Sqaured - 0.8944

But let's try it using R.

R Code: