All apportionable income shall be apportioned to this state by multiplying the income by the sales factor. [1965 c.152 § 10; 1989 c.626 § 5; 1989 c.1088 § 1; 1995 c.79 § 156; 2001 c.793 § 1; 2003 c.739 1,5; 2005 c.832 48,49; 2009 c.842 § 1; 2017 c.43 § 4]