[Actuarial Math] Company ABC is required to pay their customers $20,000 after 3 years. Based on an annual effective interest rate of 4%, Andy, the companys actuary, uses full immunization strategy to construct a portfolio of assets using a 2-year zero-coupon bond and a 4-year zero-coupon bond. Calculate the par amount for the 2-year zero-coupon bond assuming full immunization is met.