Please explain thoroughly. :)

C  =  5n + 40

        ______     multiply both sides by 9

            9

9C  =  5n + 40       subtract 40 from both sides

9C - 40  =  5n       divide both sides by 5

9C - 40

______    = n      notice that we can split th left side up as

     5

9C              40

___     -      __             =     n

  5               5

(9/5)C  -  8  = n           answer  "A"

Tysm :D