(a) For taxable years beginning on and after January 1, 2018, the West Virginia adjusted gross income of a taxpayer who is a shareholder of an S corporation, or member of a limited liability company, engaged in business as a financial organization as defined in §11-24-3a(a)(14) of this code, as adjusted pursuant to §11-21-12 of this code, shall be further adjusted by multiplying that portion of the taxpayers West Virginia adjusted gross income attributable to the taxpayers proportional share of all items of income, loss, deduction or credit of the S corporation, or limited liability company, as shown on the K-1 received by the taxpayer for the tax year, by a fraction equal to one minus a fraction:
(1) The numerator of which is the sum of the average of the monthly beginning and ending account balances of the S corporation, or limited liability company, during the taxable year (account balances to be determined at cost in the same manner that obligations, investments and loans are reported on Schedule L of Federal Form 1120S, or Schedule L of Form 1065) of the following: