Charles and Marcia are married cash$-$basis taxpayers. In $2024,$ they had interest income as follows:

$$500$ interest on federal income tax refund

$$600$ interest on state income tax refund

$$800$ interest on federal government obligations

$$1,000$ interest on state government obligations

What amount of interest income is taxable on Charles and Marcia's $2024$ joint income tax return?

$$500$

$$1,900$

$$2,900$

$$1,100$