Answer:
0.0907 = 9.07% probability that the demand will exceed 240 cfs during the early afternoon on a randomly selected day.
Explanation:
Exponential distribution:
The exponential probability distribution, with mean m, is described by the following equation:

In which
is the decay parameter.
The probability that x is lower or equal to a is given by:

Which has the following solution:

The probability of finding a value higher than x is:

Exponential distribution with mean 100 cfs (cubic feet per second):
This means that

(a) Find the probability that the demand will exceed 240 cfs during the early afternoon on a randomly selected day.

0.0907 = 9.07% probability that the demand will exceed 240 cfs during the early afternoon on a randomly selected day.