$(1$ point$)($Exercise $2\mathrm{.}1)$ In return for payments of $$2000$ at the end of $6$ years and $$6000$ at the end of $10$ years, an investor agrees to pay $$3000$ immediately and make an additional payment at the end of $4$ years. Find the amount of the additional payment if i$(6)=0\mathrm{.}08$