we know that
scale factor=1 in/7.5 ft
scale factor=measurements on the blueprint/measurements in the actual
measurements on the blueprint=[measurements in the actual*scale factor]
so
for 18 ft
measurements on the blueprint=[18 ft*(1 in/7.5 ft)-----> 2.4 in
for 16 ft
measurements on the blueprint=[16 ft*(1 in/7.5 ft)-----> 2.1 in
the dimensions on the blueprint are
2.4 in x 2.1 in