c
$v _{ rms } \propto \sqrt{ T }$
$\frac{ v _1}{ v _2}=\sqrt{\frac{ T _1}{ T _2}}$
$=$ let initial speed is $v$
As speed is increased by $3$ times so final speed become $4 v$
$\Rightarrow \frac{v}{4 v}=\sqrt{\frac{223}{T}}$
$T=3568\,K$
So temp. in ${ }^{\circ} C =3568-273=3295^{\circ}\,C$