Answer:
86.40 = c + 0.08 c is the equation which can be used to find the cost of the coat, c, without the Sales tax
Explanation:
Let us assume the cost of the coat = c
Selling price of coat = $86.40
The sale tax on the coat = 8%
⇒ The sale tax = 8% of c
Calculating the sales tax, we get:

or, the sales tax amount on the cost price of coat = 0.08 c
Now, the Sales Price of coat =Cost Price of Coat + sales Tax Amount
⇒ $86.40 = c + 0.08 c
Hence, 86.40 = c + 0.08 c is the equation which can be used to find the cost of the coat, c, without the Sales tax.