A scale drawing of a building has the scale of 0.5 inches : 6 feet. A wall is 30 feet long. How many inches long will the wall be on the drawing?

The wall will be ##2 1/2## inches long on the drawing
Using ratio:
Write 0.5 inches to 6 feet as:
##” “0.5/6##
Let the unknown scale down size be ##x##
Then we have:
##” “color(brown)(0.5/6=x/30)##
To get ##x## on its own multiply both sides by 30
##color(brown)(0.5/6=x/30)” “->” “color(brown)(color(blue)(30xx)0.5/6” “=” “(color(blue)(30))/30 xx x)##
But ##30/30=1##
##” “(30xx0.5)/6=1xx x##
##” “x=2 1/2##