3. In certain nerve cells, spontaneous electrical discharges are observed which are so rhythmically repetitive that they are called \"clock-spikes." The timing of these spikes, even though remarkably regular, does exhibit variation. In one study the inter-spike time intervals ( in milliseconds) for a housey were observed to follow approximately a normal distribution with mean 15.6 ms and standard deviation 0.4 ms. Based on this information what percentage of inter-spike time intervals will be: a) less than 15.6 ms? b} less than 16.6 ms? c) between 15.1 ms and 16.1 ms? d} Find the 95th percentile of inter-spike time intervals