Energy ,E= Sqrt{Energy intensity*Speed of light*Magnetic constant}
Where,
Energy intensity = 1.40 kW/m^2 = 1400 W/m^2
Speed of light = 3*10^8 m/s
Magnetic constant = 4pi*10^-7 H
Therefore,
E= Sqrt{1400*3*10^8*4*pi*10^-7} = 726.49 v/m
Now,
Emax = E*sqrt (2) = 726.49*Sqrt(2) = 1027.41 v/m