It is given that 

 $\overrightarrow{E}=6.6\hat{j}( \mathrm{V} {\mathrm{m}}^{-1})$.

The relation between the electric, magnetic field and speed of light is $\overrightarrow{E}\times \overrightarrow{B}=\overrightarrow{c}$.

Clearly,   $\overrightarrow{B}=B_0\left(\hat{k}\right)$

Using the relation,
     $c{B}_0=E$
$\Rightarrow B_0=\left(\frac{E}{c}\right)=\frac{6.6}{3\times {10}^8}=2.2\times {10}^{-8} \mathrm{T}$