25.46 Mastering Physics part B,C vs 25.44

to find the intensity, I used:
I1= c (8.85*10^-12) E^2 ---> part B
I2= c * B^2 /(4pi*10^-7) ---> part C

and finally got it right

but in the problem 25.44,
the Imax is given and Emax is asked
when I used the formula above I got it wrong, turned out needed to multiply by sqrt2 to get max value.

which formula is correct?

thanks