The slope-intercept form of a line equation is given by:
[tex]y=mx+b[/tex]Where m is the slope of the line and b is the y-intercept. From the problem, we identify:
[tex]m=-0.6[/tex]To find b, we use the fact that when x = 20, y = 13:
[tex]\begin{gathered} 13=(-0.6)20+b \\ 13=-12+b \\ \\ \Rightarrow b=25 \end{gathered}[/tex]Finally, for x = 16 (the corresponding y is the height of the candle after 16 hours):
[tex]\begin{gathered} y=-0.6(16)+25=-9.6+25 \\ \\ \therefore y=15.4\text{ cm} \end{gathered}[/tex]