II、計算問答題(每大題 10 分，共 20 分。) 1. Mary has T = 40 observations on variables y, x_1, and x_2. She estimates the following equations by least squares: Residual sum of squares (SSR)=140, R^2 = 0.8 where the numbers in parentheses are standard errors. What is the true value of SST in equation (1)? What is the value of s^2 (estimated error variance.)?