For the purpose of calculating Pennsylvania qualified research and development expense used in calculating the Pennsylvania base amount for taxable years ending after 1991 and before 1997, if the taxpayer has incurred qualified research and development expense both inside and outside this Commonwealth and is unable to determine the amount of Pennsylvania qualified research and development expense, the taxpayer may calculate Pennsylvania qualified research and development expense by multiplying qualified research and development expense everywhere by the average of the payroll and property factors calculated in accordance with Article IV of this act for the corresponding taxable years in question.
72 P.S. § 8708-B