Question

A channel is permeable to both sodium and potassium. If theexternal cation concentrations are 110 mM Na and 5 mM K, and theinternal concentrations 10 mM Na and 110 mM K, and the sodiumconductance is one quarter of the potassium conductance, what isthe reversal potential of the channel?

I've calculated the equilibrium potentials for sodium andpotassium but I do not know now to proceed with calculating thereversal potential because I don't have exact numbers for theconductance of sodium or potassium. Help please!