The complete question in the attached figure
we know that
perimeter=24 ft
[the perimeter of a rectangle]=2*8+2*x-----------> 16+2x
24=16+2x-------> 2x=24-16----------> 2x=8----------> x=4 ft
the answer is
the option C) x=4 ft
we know that
perimeter=24 ft
[the perimeter of a rectangle]=2*8+2*x-----------> 16+2x
24=16+2x-------> 2x=24-16----------> 2x=8----------> x=4 ft
the answer is
the option C) x=4 ft