Answer:[tex]3(2y-1)[/tex]
Step-by-step explanation:
Given
Length is increasing at the rate of [tex]\dot{x}=6\ ft/s[/tex]
Width is decreasing at the rate of [tex]\dot{y}=3\ ft/hr[/tex]
Area is given by
[tex]A=xy[/tex]
So rate of area is
[tex]\frac{dA}{dt}=x\frac{dy}{dt}+y\frac{dx}{dt}[/tex]
[tex]\frac{dA}{dt}=x\times (-3)+y\times (6)[/tex]
[tex]\frac{dA}{dt}=6y-3x[/tex]
[tex]\frac{dA}{dt}=3(2y-1)[/tex]
So, area is changing at the rate of [tex]3(2y-1)[/tex]