Because, if 6 + 6 = 12, then in 6 + 7, 7 can be splitted into 6 + 6 + 1, and so you find it easier...!!
Ratio and proportion
height:shadow=1.5:2
for the building, shadow=24
1.5:2=h:24
1.5/2=h/24
multiply both sides by 24
36/2=h
18=h
the building is 18 meters
