Exponential distribution with an unknown parameter, theta

I don't actually know what topic this falls under exactly to be honest. The question goes:

*In an experiment to study pulses along a nerve fibre, the times between 101 successive pulses were measured. The observations gave a sample mean seconds. Assuming that these data are a random sample from an exponential distribution, calculate*

**(i)** the most likely value for the mean pulse rate per second

**(ii)** the most likely value for the probability that the time between successive pulses is greater than 20 seconds i.e. .