Question 697883
Your mistake was dividing (100 square feet)/(6 inches).
 
The area of the kitchen floor can be calculated as you did:
(12 feet)*(10 feet) - (4 feet)*(5 feet) = 120 sq. feet - 20 sq. feet = 100 sq. feet,
but you have to pay attention to the units.
If you knew the area covered by each tile in square feet, you could divide by that number to figure out how many tiles are needed.
Unfortunately, you are not told the area covered by each tile in square feet.
The problem gives you the shape of the tiles (square) and the length of their sides (6 inches).
 
There are several possible ways to proceed:
 
You could figure out that since 1 foot is 12 inches = 2*(6 inches),
you need 4 tiles to cover 1 square foot.
{{{drawing(300,300,-6.5,8.5,-8,7,
rectangle(-6,-6,6,6),
line(-6,0,6,0),line(0,-6,0,6),
locate(-5.8,-2.5,6),locate(-5.3,-2.5,inches),
locate(-5.8,3.3,6),locate(-5.3,3.3,inches),
locate(-4.2,5.8,6),locate(-3.7,5.8,inches),
locate(1.8,5.8,6),locate(2.3,5.8,inches),
locate(-0.8,-6.2,1), locate(-0.1,-6.2,ft),
locate(6.2,0.5,1), locate(6.9,0.5,ft),
arrow(-1.1,-6.5,-6,-6.5),arrow(1.1,-6.5,6,-6.5),
arrow(7,0.6,7,6),arrow(7,-0.6,7,-6)
)}}}
Next, you could calculate (a) the number of tiles, or (b) the price per square foot of tiles/tiled floor. I like those choices.
To find the number of tiles, you just multiply square feet of floor times 4 to get
(100 sq ft)*(4 tiles/1 sq. ft) = 400 tiles.
Then you just multiply (400 tiles)*($1.50/tile) = $600.
To find the price per square foot of tiled floor, you figure out (4 tiles/sq. ft)*($1.50/tile) = $6/sq. ft,
and then (100 sq ft)*($6/sq. ft) = $600
  
Otherwise, you could calculate the area covered by 1 tile in square feet (1/4 sq. ft, or 0.25 sq. ft), and then divide the floor area in sq. ft by the tile area in sq. ft:
{100 sq ft)/(0.25 sq. ft/tile) = 400 tiles.
 
Calculating the area of the floor and the area of each tile in square inches is another option, but the numbers get too large and cumbersome.