Temperature of a star via its flux

[cwolfx2]

Homework Statement

What is the temperature of a star if the flux at 450 nm is measured to be 1.3 times the flux at 650 nm

Homework Equations

To determine monochromatic flux I use:

2πhv³/c²
e^x-1

x= hv/kT

The Attempt at a Solution

So basically I plug in the 450 or 640 nm wave lengths for v and using the other constants I try to guess a temperature that when I combine the individual monochromatic fluxes, they will equal 1.3

However I am using values from 5-50000 kelvin for my temperature, and I don't seem to be getting closer to 1.3, what am i missing?

 

[cwolfx2]

So I've tried this: v³(e^hv'/kt)-1= 1.3
(e^hv/kt-1) v'³

where as the ' notes the other wavelength..Also how do i turn the nm into frequency?