Answer
a. 330 $\Omega$
b. 8.9 $\Omega$
Work Step by Step
a. When resistors are wired in series, we use equation 19–3 to find the equivalent resistance.
$$R_{eq}=3(45\Omega)+3(65\Omega)=330\Omega$$
b. When resistors are wired in parallel, we use equation 19–4 to find the equivalent resistance.
$$\frac{1}{R_{eq}}=\frac{1}{45\Omega}+\frac{1}{45\Omega}+\frac{1}{45\Omega}+\frac{1}{65\Omega}+\frac{1}{65\Omega}+\frac{1}{65\Omega}$$$$R_{eq}=8.9\Omega$$