John paid $32.16 for groceries this included the 7% sales tax what was the cost of groceries before the sales tax

The answer is $30.06.

John added 7% of tax to the price before tax which is 100%. So, the price John paid is 107%. If $32.16 is 107%, how many $ is 100% (the price before tax):

$32.16 : 107% = x : 100%

After crossing the products:

x · 107% = $32.16 · 100%

⇒ x = $32.16 · 100% : 107% = $30.06

Therefore, the cost of groceries before the sales tax is $30.06.