The scale 0.5 in : 6 ft, means that
any distance of 0.5 in on paper, represents 6 ft in reality
for example:
0.5*2= 1(in) represents 6*2=12 (ft)
0.5*4= 2(in) represents 6*4=24 (ft)
0.5*10=5(in) represents 6*10=60 (ft) and so on...
Let the wall be x (in) in the drawing:
0.5 (in) represents 6 (ft),
x (in) represents 30 (ft)
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thus x = (0.5*30)/6 = 15/6= 2.5 (in)
Answer: 2.5 in