The depth of water, in metres, at a certain point in a harbour varies with the tide and can be modelled by a function of the form f(t) = a + bcosct
where t is the time in hours from the first high tide on a particular Saturday and a, b, and c are constants. (Note: ct is expressed in radians.)

On that Saturday, the following were noted:
The depth of the water in the harbour at high tide was 5.5 m
The depth of the water in the harbour at low tide was 1.7 m
• High tide occurred at 02:00 and again at 14:34.

Find the values of a and b