15. The height of an ocean tide may be modelled by the equation h(t) = -2(t - 1)(t -3), where h represents the water's height in metres above an island at t hours. For example, if h(t) is zero, the tide is at the island's level, and if h(t) is negative, the tide is below the island. Between which hours is the island submerged by ocean water, and for how long is it submerged? Mark Value: 316. Determine the coordinates of the hole in the following rational function: x(x+1)(x -4) f (x) = 2x: (x+ 4) (a) (0, -2) Mark Value: 3 (b) (45) (c) (0.-1) (d) (-4, - -) 17. For which interval of * is the function f(x) = log(x - 1) positive? (a) x1 (b)=> 1 (9)12 Mark Value: 3