In order to find your solution, first you need to convert 7 quarts to fluid ounces so your units are correct when you finally solve.
1 quart= 32 fl oz so 7 quarts= 224 fl oz
Then you take the window cleaner cost ($31.36) and divide it by the 224 fl oz of window cleaner.
31.36/224=$0.14
For every fl oz it will cost $0.14