Mary saved $61 by purchasing the tires through the mail
Solution:
Total for the 4 tires by mail order
= 4 x (57.60 + 4.30 + 7.58)
= 277.92
She paid $ 57.60 per tire
She paid $ 4.30 per tire for shipping and handling
She paid $ 7.58 including tax, per tire for mounting and balancing.
6% sales tax
At a local tire store, her total for the 4 tires
= $ 320 + 6% x 320
= 339.2
∴ 339.2 - 277.92= 61.28 ≈ $61
Mary saved $61 by purchasing the tires through the mail