To determine the frequency of a wave that has a period of 18 seconds, we use the relationship between period (T) and frequency (f):
[tex]\[ f = \frac{1}{T} \][/tex]
Here, the period [tex]\( T \)[/tex] is given as 18 seconds. Substitute [tex]\( T \)[/tex] with 18 seconds into the formula:
[tex]\[ f = \frac{1}{18} \][/tex]
Performing this division, we get:
[tex]\[ f = 0.05555555555555555 \][/tex]
Now, we compare this result with the given choices. The correct match is:
B. [tex]\( 5.5 \times 10^{-2} \)[/tex] hertz