This year, Randy paid $28,000 of interest on his residence. (Randy borrowed $450,000 to buy his residence, and it is currently worth $500,000.) Randy also paid $2,500 of interest on his car loan and $4,200 of margin interest to his stockbroker (investment interest expense). How much of this interest expense can Randy deduct as an itemized deduction under the following circumstances?

a. Randy received $2,200 of interest this year and no other investment income or expenses. His AGI is $75,000.

b. Randy had no investment income this year, and his AGI is $75,000.

PLEASE EXPLAIN HOW YOU REACHED YOUR ANSWERS SO I CAN LEARN HOW TO GET THERE ON MY OWN.