An electromagnetic wave travelling in x -direction is described by...

The maximum electric force acting on the electron is $F_e = eE_0$.

The maximum magnetic force acting on the electron is $F_m = evB_0$, where $v$ is the speed of the electron and $B_0$ is the maximum magnetic field.

The ratio of the maximum electric force to the maximum magnetic force is given by $\dfrac{F_e}{F_m} = \dfrac{eE_0}{evB_0} = \dfrac{E_0}{vB_0}$.

For an electromagnetic wave, the ratio of the amplitudes of the electric and magnetic fields is $\dfrac{E_0}{B_0} = c$, where $c$ is the speed of light in vacuum.

Substituting this into the ratio of forces yields $\dfrac{F_e}{F_m} = \dfrac{c}{v}$.

Given $c = 3 \times 10^8$ m/s and $v = 1.5 \times 10^6$ m/s, we get $\dfrac{F_e}{F_m} = \dfrac{3 \times 10^8}{1.5 \times 10^6} = 200$.

Answer: $200$