Answer
The equivalent resistance is $~~30.0~\Omega$
Work Step by Step
If we imagine that a battery is connected between B and C, the current could flow across the left resistance, and then across either the middle resistance or the right resistance. Therefore the middle resistance and the right resistance are in parallel.
We can find the equivalent resistance of the middle and the right:
$\frac{1}{R_{eq}} = \frac{1}{20.0~\Omega}+\frac{1}{20.0~\Omega}$
$\frac{1}{R_{eq}} = \frac{2}{20.0~\Omega}$
$R_{eq} = \frac{20.0~\Omega}{2}$
$R_{eq} = 10.0~\Omega$
Then the equivalent resistance of the circuit is $~~10.0~\Omega+20.0~\Omega = 30.0~\Omega$
The equivalent resistance is $~~30.0~\Omega$
