Answer:
[tex]\frac{dx}{dt} = 10 ft/s[/tex]
Explanation:
As per given figure let say the tip of the shadow is at distance "x" from the base of the lamp
so here we have
[tex]\frac{x}{15} = \frac{x - y}{6}[/tex]
so we have
[tex]6x = 15 x - 15 y[/tex]
[tex]15 y = 9 x[/tex]
now we have
[tex]5\frac{dy}{dt} = 2\frac{dx}{dt}[/tex]
[tex]5(4) = 2\frac{dx}{dt}[/tex]
[tex]\frac{dx}{dt} = 10 ft/s[/tex]
