Answer:
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]