Afast food restaurant sold 64 burgers with cheese. if the ratio of burgers sold with cheese compared to without cheese was 8 : 1, how many burgers did they sell total?

Total number of burgers sold by the restaurant with cheese = x
Ratio of the total number of burgers
 with cheese to total number of burgers without cheese = 8 :1
Let us assume the common ratio to be = x
then
8x = 64
x = 64/8
  = 8
So
The number of burgers sold without cheese = 8 * 1
                                                                       = 8
Then
The total number of burgers sold by the fast food restaurant = 64 + 8
                                                                                                 = 72
So the total number of burgers sold by the fast food restaurant is 72. I hope the procedure is clear enough for you to understand.

Where is the expression you want us to evaluate?