The $7 more than Vivian would have paid represents 2% of the price of her purchase--the difference between 6 percent and 8 percent. So, we can find the price of her purchase:
0.02p = 7
(1/50)p = 7
p = 7(50) = 350
We're looking for what she paid including sales tax. Sales tax is 6 percent:
t = 0.06(350) = 6(3.5) = 21
The total price, then, is 350 + 21 = 371, choice (B).