The electric fields arriving at a point $P$ from two sources are described by $E_1=12coswt,E_2=10cos(\frac{n}{4}-wt).$ Assume the resultant field is represented by $E_R=E_{0R}cos(-wt).$ The amplitude of the resultant wave at $P$ is

Select one:

a$.10\frac{V}{m}$

b$.20\mathrm{.}3\frac{V}{m}$

c$.13\mathrm{.}2\frac{V}{m}$

d$.15\mathrm{.}6\frac{V}{m}$