what is the rms value of an ac which when passed through a resistor produces heat which is thrice of that produced by dc of 2 A in the same resistor?

sir in this question after equating H= I^2R(T/2) and H= I^2RT ; i am getting the answer as 2.45 A but the correct answer is 3.46.

Please explain this sir... plz as soon as possible.