A regression model between sales (y in $1000s), unit price (x₁ in dollars) and television advertisement (x₂ in dollars) resulted in the following function: = 7 3x₁ + 5x₂ For this model, SSR = 3500, SSE = 1500, and the sample size is 18. If we want to test for the significance of the regression model, the critical value of F at 95% confidence is _____.

a. 4.54

b. 3.29

c. 3.68

d. 3.24