RLC circuit, at what frequencies is the current 0.8A
Yes, your understanding is correct.

You know that the magnitude of the circuit impedance needs to be 12.5 ohms for the current to be 0.8A.

So, write down the equation for the magnitude of the total impedance of all three components as a function of frequency, set it equal 12.5 ohms, and solve for f. It's a quadratic equation, so you will indeed get two answers.