electrical circuit

A 72-ohm coil of wire is connected in series with an adjustable resistor (rheostat) whose resistance can be varied from 0 to 88 ohms. If the line potential is 115 volts, calculate (a) the range through which the coil current can be varied, (b) the rheostat resistance when the power taken by the coil is 90 watts

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  1. i've gotten (a) 0.72 to 1.6 amp; (b)17.7 ohms

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  2. a is right on both accounts but I don't get your answer for b.
    P = E*I
    90/115 = I
    R = E/I = 115/I from above. I get about 147 ohms and subtract 72 from that.

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