Can anyone help me with this question, I'm unsure on where to start 

Tides vary so the high tide and low tide height of the water is different every day. At certain times of the year, such as a Spring tide, the water can be very deep and it may not be safe to cross the inlet. During one big tide, the water was 3.9 metres deep at high tide and 0.7 metres deep at low tide. The Department of Conservation (DOC) recommends that walkers only cross the inlet within one and a half hours before low tide and two hours after low tide. Find a safe time to cross the inlet during this big tide and discuss DOC’s recommendation in relation to your findings for both tidal situations. 

 

2 hours ago, 1845 said:

Can anyone help me with this question, I'm unsure on where to start 

Tides vary so the high tide and low tide height of the water is different every day. At certain times of the year, such as a Spring tide, the water can be very deep and it may not be safe to cross the inlet. During one big tide, the water was 3.9 metres deep at high tide and 0.7 metres deep at low tide. The Department of Conservation (DOC) recommends that walkers only cross the inlet within one and a half hours before low tide and two hours after low tide. Find a safe time to cross the inlet during this big tide and discuss DOC’s recommendation in relation to your findings for both tidal situations. 

 

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Apply trigonometric methods in solving problems

This looks like homework/coursework and should be placed in that section.

 

You should start by reading the instructions. The clue is in the instructions.

What trigonometric functions do you know that have an maximum and a minimum (and for the sake of learning which ones do not) ?
They must be pretty simple ones since you are only told the  max and min.

You must have been told something else about the timing as you will need the time difference between high and low tide to match the angular distance to the time distance on your trigonometric model.