Answer: [tex]49x^2-42x+9[/tex]
Explanation: The area of a square is determined by the length of its side. In this case, the length of the side varies with an unknown variable x, therefore the area will also be a variable (dependent on x in a quadratic way):
[tex]A=(7x-3)(7x-3)=49x^2-42x+9[/tex]
Example: if x is 1:
[tex]x=1\implies\,\,\mbox{side}=4 \,\,\mbox{ft}\\49\cdot 1^2-42\cdot 1+9=16 \,\,\mbox{sq.ft}[/tex]
