7.5\Omega
\begin{circuitikz}
\draw (0,0) to[R, l_=5\Omega] (2,0);
\draw (2,0) to[R, l_=15\Omega] (4,0);
\draw (4,0) to[R, l_=15\Omega] (6,0);
\draw (6,0) to[R, l_=7.5\Omega] (6,2);
\draw (6,2) to (2,2);
\draw (2,2) to (2,0);
\draw (2,0) to[R, l_=10\Omega] (2,-2);
\draw (4,0) to[R, l_=10\Omega] (4,-2);
\draw (2,-2) to (4,-2);
\draw (0,0) to[short, -triangle 60] (-1,0);
\draw (-1,0) to (-1,-2);
\draw (-1,-2) to (4,-2);
\draw (0,-2) node[left] {$R_{eq}$};
\end{circuitikz}
