A candle burns at a constant rate of 2.5cm/h. The candle is 15cm tall when it is first lit. Let "t" represent the time is it burning in hours and let "h" represent the height of the candle in centimetres.

The initial height of the candle is H = 15cm

The rate at which the candle burns is 2.5 cm per hour

Then after one hour, the height of the candle is:

h = 15cm - 2.5cm = 12.5cm

after two hours is:

h = 15cm - 2*2.5cm = 10cm

then, after t hours, the height of the candle is:

h = 15cm - (2.5cm/h)*t

now, the domain of h (or the range of the function) is:

h ∈ [0cm, 15cm]

when t = 0, h(0h) = 15cm

and the maximum value of t will be such that the candle is totally consumed:

h(t) = 0 = 15 - 2.5*t

t = 15/2.5 = 6

Then the domain of the function is:

t ∈ [0h, 6h]