You entered the total dividends, from the Vanguard fund, at the 1099-DIV screen. After doing so, you get a screen titled "Tell us if any of these uncommon situations apply to you". Check the box "A portion of these dividends is US Government interest". The follow up screen is "Enter US Government interest". Enter your manually calculated amount in the box at that screen. That amount will automatically carry to the state return, for the deduction.
