Given that the height of a candle (in centimeter) is a linear function of time (in hour) it has been burning.
Let at time t, the height of the candle be h
Since h is a linear function of t, let us assume
[tex]h=at+b[/tex]
After 6 hours of burning, the candle has a height of 19.4 centimeters.
After 20 hours of burning, its height is 11 centimeters.
So, the line representing h passes through the points (6,19.4) and (20,11)
Using two-point formula
[tex]\begin{gathered} \frac{h-11}{19.4-11}=\frac{t-20}{6-20} \\ \frac{h-11}{8.4}=\frac{t-20}{-14} \\ h=-\frac{3}{5}t+23 \end{gathered}[/tex]
So, the height of the candle is
[tex]h=-\frac{3}{5}t+23[/tex]
Now, putting t=8, it gives
[tex]\begin{gathered} h=23-\frac{3}{5}\times8 \\ =23-\frac{24}{5} \\ =\frac{115-24}{5} \\ =\frac{91}{5} \end{gathered}[/tex]
So, after 8 hours, the height of the candle is 18.2 centimeters.