Answer
Connect $521\Omega$ and $146\Omega$ in series and then connect this pair in parallel with $413\Omega$.
Work Step by Step
We should connect $521\Omega$ and $146\Omega$ in series and then we should connect $413\Omega$ in parallel to obtain the required equivalent resistance $255\Omega$. This is shown as follows:
$R{eq_1}=521+146=667$
Now $R_{eq}=(\frac{1}{667}+\frac{1}{413})^{-1}$
$R_{eq}=255\Omega$
