I'm assuming the blueprint shows 1 inch is equal to 10 ft. This means that 1 inch on the blueprint corresponds to 10 feet in real life.
We have the ratio
1 inch: 10 feet
If we multiply both sides by 0.5 then,
0.5*(1 inch) : 0.5*(10 ft)
0.5 inch : 5 feet
So 0.5 inches (aka half an inch) on the blueprint corresponds to 5 feet in real life.
Answer: A) 5 feet
