In a three-phase balanced system, a delta-connected source supplies power to a wye-connected load. If the line impedance is $0.2+j 0.4 \Omega,$ the load impedance $6+j 4 \Omega$, and the source phase voltage $\mathbf{V}_{a b}=210 / 40^{\circ} \mathrm{V} \mathrm{rms},$ find the magnitude of the line voltage at the load.