Given resistance of $1 \Omega, 2 \Omega$ and $3 \Omega$ how will we combined them to get an equivalent resistance of $6 \Omega$

Question

$\begin{array}{1 1} \text{All the three resistance in series } \\ \text{All the three resistance in parallel } \\ \text{R1 and R2 in series and then equivalent in parallel with R3} \\ \text{R1 and R2 in parallel and then equivalent in series with R3} \end{array}$