The units are the complete story on this question. All of the choices are over 1 so the units make the answer over one. It takes more feet than it does inches to make the scale. The correct units are 120 feet / 3 inches. That makes A and B both incorrect.
You can't get 360 by any method but multiplication. The units for multiplication would be ft*in. So D is wrong. That only leaves you with C which is the answer.
Original price: $40 Sale Price: $32 Total changes: $8 Take the amount increase/decrease and times divide by the original amount and times by 100 8/40=.2 x 100= 20% or 10% of 40 is 4 20% of 40=8 so The percent was 20%