Input data
Mary purchased
4 tires
$ 63.10 per tire
$ 5.20 per tire shipping
$ 7.76 per tire for mounting
Mary's total for the 4 tires with mounting and balancing would be $340 plus 8% sales tax.
Procedure
Total in mail
[tex]\begin{gathered} T=4(63.10+5.20+7.76) \\ T=4(76.06) \\ T=304.24 \end{gathered}[/tex]Total in local store
[tex]\begin{gathered} T_s=340+340\cdot8\text{ \%} \\ T_s=340+27.2 \\ T_s=367.2 \end{gathered}[/tex]The difference between the two forms of purchasing is
[tex]\begin{gathered} T_s-T=367.2-304.24 \\ T_s-T=62.96 \end{gathered}[/tex]Mary saved a total of $62.96