An AC adapter for a telephone answering machine uses a transformer to reduce the

Question

An AC adapter for a telephone answering machine uses a transformer to reduce the line voltage of 120 V to a voltage of 9.00 V. The RMS current delivered to the answering machine is 690 mA. a. If the primary (input) coil of the transformer has 720 turns, then how many turns are there on the secondary (output) coil?
b. What is the power drawn from the electric outlet, if the transformer is assumed to be ideal?
c. What is the power drawn by the transformer, if 14.5 percent of the input power is dissipated as heat in the coils and in the iron core of the transformer?

I figured out parts a to be 54 turns and b to be 6.21 W but I could not figure out part c.
I did Powerdissipated + Poweruseful = Powerdrawn so I did (.145)(6.21) + (6.21) = 7.1104 W
but it came out as the wrong answer. I only have 7 tries left. Please help.

Explanation / Answer

Part (c) is 7.263 watts. You were close. The calculation you want to make is : (1 - 0.145)x = 6.21 0.855x = 6.21 x = 6.21/0.855 = 7.263 You are looking for the number such that when you take 14.5 percent away, the answer is 6.21.

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