If P stands for perimeter of the rectangle then you have performed the correct calculation. Perimter is a measure of distance so the answer 33 is meaningless unless you mention the units (feet). The perimter of the rectangle is 33 ft.
I have a retangle that is 12 ft by 4 1/2 ft
P= 12x 2 + 2 X 4 1/2=
24 +9 = 33
P = 33
I do not know Geometry , if this is correct, please let me know , if not please let me know how I made the mistake
Steven