7. Given the results below for a sample of 14 observations, answer the following questions. yt=1+2x2t+3x3t+4x4t+tR2=0.80yt=1+2x2t+4x4t+fR2=0.71yt=1+2x2t+3x3t+rR2=0.72yt=1+2x2t+tR2=0.69 a) Test that 3=0 with 90% confidence. b) Test that 4=0 with 90% confidence. c) Test the joint hypothesis that 3=0 and 4=0 with 90% confidence