A transformer for charging a power tool steps the line voltage down to 2.9 V.

The output current of this transformer is 240 mA. If the transformer is 80% efficient, what is the input current?
A)7.3 mA
B)240 mA
C)4.6 mA
D)190 mA
E)300 mA

If you could walk me through the steps, that would be great!

Output power is 2.9 volts x 240 ma = 0.696 watts
input power is 0.696 watts / 0.8 = 0.87 watts

assuming 120 volts line voltage, input current is 0.87 watts / 120 = 7.25 mA (a)

If the line is 240 volts, input current is 3.63 mA

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