My salary is $53,000. I got an inheritance for $20,000. I have exemptions and deductions for $5,000. What is my AGI?

This definitely sounds like a homework question, because the exemptions and deductions are NOT up to the modern personal exemption amounts of $3,800 for personal exemption and $5,800 for the standard deduction.

That said, your AGI is $48,000. The inheritance is NOT subject to income taxes and thus NOT part of your AGI.