#### Answer

a) $2$.
b) $2$.
c) $12$ hours.

#### Work Step by Step

a) The high tides are represented by the points of the graph with the highes value, in other words the peaks. We can see that this graph has two peaks. Therefore, the number of high tides is $2$.
b) The low tides are represented by the points of the graph with the lowest value. We can see that this graph has two minimal turning points. Therefore, the number of low tides is $2$.
c) The time elapsed in between a high tides is represented by the interval starting at the peak of the first high tide (10 hrs) and ending at the peak of the second high tide (22 hrs). Next, we subtract the first value from the second value to receive the time in between the high tides: $ 22 $hrs $- 10$hrs = $12$hrs.