What is the equivalent resistance of the following combination of resistors?

Three resistors with resistances $R_1$ = $2$ $\Omega$, $R_2$ = $4$ $\Omega$, and $R_3$ = $6$ $\Omega$ are connected in series. What is the equivalent resistance of the resistor network?

Given four circuits, each containing three identical resistors of resistance $R$, which arrangement results in the smallest equivalent resistance?

Three resistors with resistances $R=2\Omega$, $R=4\Omega$, and $R=6\Omega$ are connected in series to a $12V$ battery. What is the current through the $4\Omega$ resistor?

What is the equivalent resistance of the following combination of resistors?

If every resistor below has resistance R, what is the equivalent resistance of the combination, in terms of R?