The circuit below includes a real battery with an emf $$ and an internal resistance $r=1\mathrm{.}8,$ a resistor $R,$ an ideal ammeter, an ideal voltmeter, and a switch $S.$ When the switch $S$ is open, the voltmeter shows a reading of $9$ V $.$ When the switch $S$ is closed, the ammeter reads $1\mathrm{.}5$ A $.$ What is the value of $R?$

$2\mathrm{.}4$

$4\mathrm{.}2$

$7\mathrm{.}8$

$6\mathrm{.}0$

$1\mathrm{.}4$