Answer:
15 in - (1.25 in/hr)t
Step-by-step explanation:
L(t) is a function of time, t: Â L(t) = 15 in - (1.25 in/hr)t
Note that when the candle has burned down to nothing, L(t) = 0. Â How long does that take? Â Set 15 in - (1.25 in/hr)t equal to zero and solve for t:
(1.25 in/hr)t = 15 in, or
     15 in
t = ---------------- = 12 hrs
   1.25 in/hr