The relationship between demand (y) and price (x) for an electronics product was analyzed using a simple linear regression model. With n = 14 observations, the total variation of the dependent variable is obtained to SST = 83 and the residual square sum to SSE = 18. The slope parameter was estimated to be a negative value.

a) Determine the residual variance, s²_e.

b) Determine the degree of explanation R²

c) Test the hypothesis H₀: =0 against H_A: <0 with a t-test. Use the 5% signal level.