For the two cells having same EMF E and internal resistance r, the current passing through the external resistor 6 Ω is same when both the cells are…

For the two cells having same EMF $\displaystyle E$ and internal resistance $\displaystyle r$, the current passing through the external resistor $\displaystyle 6 \Omega$ is same when both the cells are connected either in parallel or in series. The value of internal resistance $\displaystyle r$ is $\displaystyle \_\_\_\_ \Omega$.