In the following figure, the resistances are R$1=2\mathrm{.}00\backslash$Omega $,$ R$2=5\mathrm{.}00\backslash$Omega $,$ the ideal battery has an emf of $12\mathrm{.}0$ V$,$ the total current is $2\mathrm{.}25$ A$.$ How many ohms of resistance is in R$3?$