Answer:
 $227.64
Step-by-step explanation:
The relevant relations are ...
 sales + tax = total
 tax = 7% × sales
Using the second equation, we can write sales in terms of the tax as ...
 sales = tax/0.07
Substituting this into the first equation gives ...
 tax/.07 + tax = total . . . . . substitute for sales
 tax(1/0.07 + 1) = total . . . . factor out tax
 tax ((1 +.07)/.07) = total . . . simplify to a single fraction
Multiply by the inverse of this fraction:
 tax = .07/1.07 × total = (7/107)($3479.64)
 tax = $227.64
