In an $L C R$ series circuit, an inductor 30 mH and a resistor $1 \Omega$ are connected to an AC source of angular frequency $300 \mathrm { rad } \mathrm { s } ^ { - 1 }$. The value of capacitance for which the current leads the voltage by $45 ^ { \circ }$ is $\frac { 1 } { x } \times 10 ^ { - 3 } \mathrm {~F}$. Then the value of $x$ is