4. (20%) Derive the normal equations(正規方程式)for the polynomial regression y=β０+β1x1+β2x2+β3x1x2.

2. Traveling between bwo areas in a city via shuttle bus is believed to take 18 minutes with a standard deviation of 5 minutes. During a period of time, the shuttle bus operated 30 times between this route. What is the probability that the average transport time was more than 25 minutes? Do you need to assume a certain prob