There are 8 white tiles. if the total cost of the white tile is $12 , what is the unit cost per white tile ?

8 white tiles, and they cost 12 altogether. 

Lets set up a proportion. 

8/12 = 1/x       Proportion is here.

Now, cross multiply 

8*x = 12*1          Multiply
8x = 12         Result

8x/8 = 12/8            Divide both sides by 8.
x = 12/8                    x equals 12/8
x= 1.5                      x equals 1.5

Now, we have our value for x, which is 1.5, and we must add units to complete the answer.

Final $1.5 per white tile