Answer:
It is -60 mV.
Explanation:
The membrane potential of a neuron is measured as the difference between its' outside and inside values and the outside value should be greater than the inside value.
fFor the newly discovered neuron with still unknown properties, measuring the outside of the neuron as 60 mV more positive or higher than the inside means that the membrane potential of the neuron is -60 mV since it is calculated as inside value - outside value.
I hope this answer helps.
