【求教】近期計量經濟學考試...可是不知道怎麼解....求救請各位大人們...

Consider the following total cost function where yt represents total cost for the t-th firm and xt represents quantity of output.
yt＝β1＋β2 xt＋β3 xt 2＋β4 xt 3＋et
（1）Compute 95％ interval estimates of the parameters.
（2）At what output price is it profitable for firms to produce？ How many firms in the sample
are producing unprofitable outputs？
（3）What parameter restrictions imply a linear average cost function？ Test these restrictions.
（4）Estimate log-log cost function of the form ln（yt）＝α1＋α1ln（xt）＋et. Does the RESET
test suggest the log-log function is preferable to the cubic？ Is the log-log cost function
reasonable from an economic standpoint？