how do i calculate a concentration ratio of oxidised to reduced cytochrome c Fe2+ to Fe3+

Question

given at 25 C and pH7
E(mV) as 100
and absorbance at 550nm as 1.5

E is relative to standard hydrogen electrode

i know im supposed ot use the nernst equation i just don't know how im supposed to use this data to something which i can use in the nernst eq

please help