Question

A Marine Weather Station reports waves along the shore that are eight seconds apart. The frequency of the waves is therefore __ Hertz.

1/8
1/4
4
8

Answer 1

"8 seconds apart" means that one wave-peak arrives every 8 seconds.
That's another way of saying that the PERIOD of the waves is 8 seconds.

Frequency = 1/period = 1/8sec = 1/8 per second = 1/8 of a Hz.