Final answer:
Marco can deduct a total of $13,690 as mortgage interest on Schedule A.
Step-by-step explanation:
To calculate the amount of mortgage interest that Marco can deduct as an itemized deduction on Schedule A, we need to determine which properties qualify for the deduction. According to the information provided, Marco paid mortgage interest on his personal home, vacation home (used only for personal purposes), mother's home (where his mother is legally liable for the debt), and rental property.
However, only the mortgage interest on Marco's personal home and rental property can be deducted as an itemized deduction on Schedule A. The mortgage interest on his vacation home and mother's home does not qualify.
Therefore, Marco can deduct the mortgage interest of $6,048 on his personal home and $7,642 on his rental property. The total mortgage interest deduction on Schedule A would be $6,048 + $7,642 = $13,690.