Walker Inc. has accumulated minimum tax credits of $740,000 from tax years prior to 2018. Below are Walker's regular tax before credits for 2018 through 2021.

2018201920202021Regular tax before credits$50,000$60,000$40,000$30,000

Complete the following table to calculate Walker's allowable minimum tax credit each year.

2018201920202021

Nonrefundable portion of minimum tax credit

Refundable portion of minimum tax credit

Total minimum tax credit used