For electromagnetic wave,

$$|\overrightarrow B | = {{|\overrightarrow E |} \over c}$$

Here $\overrightarrow B $ is magnetic field associated with EM wave

$\overrightarrow E $ is electric field associated with EM wave

c is the speed of EM wave

$$ \Rightarrow |\overrightarrow E | = c|\overrightarrow B |$$

$$ = 3 \times {10^8} \times 3 \times {10^{ - 8}}\cos (1.6 \times {10^3}x + 48 \times {10^{10}}t)$$ V/m

Direction can be determined from

Poynting vector $$ = {{\overrightarrow E \times \overrightarrow B } \over {{\mu _0}}}$$

$$\overrightarrow E = 9\cos (1.6 \times {10^3}x + 48 \times {10^{10}}t)\widehat k$$ V/m