One-ninth of all sales at a local subway is for cash. if cash sales for the week were $690, what were subways total sales? this one is not clear. i know i am missing something here.

Let us assume the total sales of the local Subway = x
Then
Total sales done by cash at the local Subway = x/9
Total cash sales for the week at the local Subway = $690
Then
x/9 = 690
x = 690 * 9
   = 6210 dollars

From the above deduction, it can be easily concluded that the total sales of the local Subway was $6210. I hope that the procedure is clear enough for you to understand.