Answer
The average rate that energy is dissipated by $R$ is $~~100~W$
Work Step by Step
In part (a), we found that $I_{rms} = 2.586~A$
We can find $P_{ave}$:
$P_{ave} = I_{rms}^2~R$
$P_{ave} = (2.586~A)^2~(15.0~\Omega)$
$P_{ave} = 100~W$
The average rate that energy is dissipated by $R$ is $~~100~W$
