Let
x-------> the length of the beat in seconds
we know that
------> inequality that represent the beats length

the solution is the interval--------> (15,∞)
the domain is all real number greater than

Find the possibles beat lengths that satisfy the inequality
a)

substitute in the inequality
-----> is true
therefore
is a possible beat length
b)

substitute in the inequality
-----> is true
therefore
is a possible beat length
c)

substitute in the inequality
-----> is true
therefore
is a possible beat length