Answer:
Option D
[tex]f(x)=15x^{2}+380x+2400[/tex]
Step-by-step explanation:
Original dimensions are as follows
Length=60 m
Width=40 m
[tex]Area=60*40=2400 m^{2}[/tex]
New dimensions
Length=(60+5x) m
Width=(40+3x) m
[tex]Area=(60+5x)\times (40+3x)[/tex]
[tex]Area=60(40+3x)+5x(40+3x)=2400+180x+200x+15x^{2}[/tex] and collecting like terms we obtain
[tex]Area=15x^{2}+380x+2400[/tex]
Therefore,
[tex]f(x)=15x^{2}+380x+2400[/tex]
