A client died in 2015 and $4,000,000 in policy proceeds were…

A client died in 2015 and $4,000,000 in policy proceeds were payable directly to his grandson. Assuming that the $4,000,000 was taxed at 40% in the client’s federal estate and that the $4,000,000 bore the estate tax, what additional GST tax is payable on the policy proceeds?