What is [tex] I_X [/tex] in terms of [tex] I_E [/tex] ? In other words, what number do you have to multiply [tex] I_E [/tex] by to get [tex] I_X [/tex]?
Then get rid of [tex] I_X [/tex] in your equation.
Finally think about what multiplication inside of a log function maps to on the outside. I'll give you a clue on the last one and it is +.