After evaluating the single regression models, Ning generated three more models, each including two of the three possible cost drivers. Select output for each of these models is as follows. R-Square 0.6076 Coefficients Standard Error T-stat P-value Intercept 198217.404 47528.23841 4.17051864 0.00240976 Marketing expenditures 1.80418879 0.757272868 2.38248175 0.04106032 Number of units sold 21.3176008 42.76944597 0.4984306 0.63013378 R-Square 0.3605 Coefficients Standard Error T-stat P-value Intercept 217217.995 69887.2802 3.10811917 0.01255689 Number of units sold 91.0309587 41.04996818 2.21756466 0.05377736 Number of salespeople -539.13738 7066.988392 -0.0762896 0.94085772 R-Square 0.5974 Coefficients Standard Error T-stat P-value Intercept 208708.801 50886.76857 4.10143553 0.00267097 Marketing expenditures 2.0529505 0.567065564 3.62030537 0.0055691 Number of salespeople 660.890248 5513.610149 0.11986525 0.907223 Was she justified in generating each of these models in the first place? Are any of these possible models valid? Explain