Several years ago, Joyce bought series EE Savings Bonds with a cost of $20,000. The bonds are now worth $60,000. Joyce cashed in $30,000 worth of bonds (i.e., half the bonds) to pay for her son's first year in college. The $30,000 proceeds were used as follows-$22,500 tuition & books; $7,500 room & board. Before considering the $20,000 interest income from these bonds, Joyce's AGI on her head of household return was $50,000. How much, if any, of the interest income must be included in her gross income?