In an unbalanced three phase system, phase current $I_a=1\angle (-90^{\circ})\: \text{pu}$ , negative sequence current $I_{b2}=4\angle (-150^{\circ})\: \text{pu}$, zero sequence current $I_{c0}=3\angle 90^{\circ}\: \text{pu}.$ The magnitude of phase current $I_b$ in $\text{pu}$ is
- $1.00$
- $7.81$
- $11.53$
- $13.00$