In a regression model involving 50 observations, the following estimated regression model was obtained: ^ hat" style="vertical-align: -3.0px;" /> = 8.6 + 2.3x1 + 3.8x2 + 6.1x3. If SSR = 360 and SSE = 129, then MSR is... O a. 90 O b. 43 O c. 120 O d. 163