[ marks] 39. 69) 1a. [2 marks) The depth of water in a port is modelled by the function d(t) = pcosqt + 7.5, for 0 S ts (it 12, where t is the number of hours after high tide. At high tide, the depth is 9.7 metres. At low tide, which is 7 hours later, the depth is 5.3 metres. Find the value of p. 1b. [2 marks] Find the value of q. 1c. [2 marks) Use the model to find the depth of the water 10 hours after high tide