21. An annuity oonsists of 4!] payments of $3011} each made at intervals of lhree months. Interest is at j1=12%. Determine the value of this annuity at each of the following times: a] mree months before le time of the rst payment; {$??3_13] h} at the time of me last payment; {351198335} 1:] at me time of the rst payment; {$521159} :21} three months after the last payment; {351151551} e] four years and three months before the rst payment. {$449331}