In 2010, Questar Corp. spun off a separate company, QEP Resources. I had stock in Questar that I purchased before this spin off. At the time of the spin off, every share in Questar Corp. was converted in to one share in Questar Corp. and one share in QEP Resources.
I've now sold off my stock in Questar Corp. (but not my QEP stock). How should I calculate the cost basis for the Questar stock purchased before the spin off of QEP?