I keep runing in circles around this optic fiber question... Please help

Hi everyone

I can not seem to get the right formulas to finish this question.
I keep on beating my head against a wall for hours now.

This is what I have.

If I could just get the wavelength( λ ) I could easily get the diameter etc.
But λ = v/f neither if which I have. WHERE v = Normalized Frequency and λ = wavelength.
I cant find a way to get Normalized frequency to just frequency and I also do not know if I can use the function λ = c/f because I dont have c (Velocity of light in vacuum) or f.

This is what I have so far and I have no idea if its of any use.

I am trying to use this function to get the diameter of the core n1; V = ( 2π / λ )(a(NA)); Where a will be the diameter of the core.

c = 2.05^-8 m/s
m = 5000m
θa = 15.3
V = 33.5 normalized frequency
B(Maximum Bandwidth) = 1.5Mhz
Source = 900nm

NA = sin(θa) = 0.2638

n = C / Cs = 300x1-^-6 / 205x10^-6 = 60/41 = 1.463


I dont know where to go from here as there is thousands of little formulas but I cant seem to pinpoint even 1 to use.

Thanks