15% of a 84.00 dollar jacket plus 7% sales tax

100-15=85

$${\mathtt{0.85}}{\mathtt{\,\times\,}}{\mathtt{84}} = {\frac{{\mathtt{357}}}{{\mathtt{5}}}} = {\mathtt{71.4}}$$

100+7=107

$${\mathtt{1.07}}{\mathtt{\,\times\,}}{\mathtt{71.4}} = {\mathtt{76.398}}$$

$76.40

15% of a 84.00 dollar jacket plus 7% sales tax

From what I understand, you mean you will get 15% off the price of the Jacket plus 7% sales tax.

So $84 - 15%(or .15 x 84)=$71.40 + 7%=$76.40 the final price you pay.