Given:
Magnetic field amplitude = 5.4 mT
Let's find the electric field amplitude of the electromagnetic wave.
To find the electric field amplitude, apply the formula:

Where:
C is the speed of light = 3 x 10⁸ m/s
B is the magnetic field amplitude = 5.4 mT = 5.4 x 10⁻³ T
E is the electric field intensity.
Plug in the values and solve for E:

Therefore, the electric field amplitude is 1.62 x 10⁶ V/m.
ANSWER:
1.62 x 10⁶ V/m.