Answer
(a) $10A$
(b) $5.0A$
Work Step by Step
(a) As $R_{eq}=(\frac{1}{R}+\frac{1}{R})^{-1}=\frac{R}{2}=\frac{15}{2}=7.5\Omega$
Now $I_{rms}=\frac{V_{rms}}{R_{eq}}$
We plug in the known values to obtain:
$I_{rms}=\frac{V_{rms}}{R_{eq}}=\frac{75}{7.5}=10A$
(b) We know that
$I_{rms}=\frac{V_{rms}}{R}$
We plug in the known values to obtain:
$I_{rms}=\frac{75}{15}=5.0A$