let's firstly convert it to an improper fraction.

Step-by-step explanation:
This sales tax table (also known as a sales tax chart or sales tax schedule) lists the amount of sales tax due on purchases between $0.00 and $59.70 for a 5% sales tax rate.
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5% Sales Tax Chart ($0.00 - $59.70)
Price 20.10
Tax 1.01
Price 30.10
Tax 2.01
Tax 2.51
The correct slope is -5/2.
The formula for slope is
m = (y₂-y₁)/(x₂-x₁)
The y-coordinate of the second point is 0, and the y-coordinate of the first point is 2. The x-coordinate of the second point is 0.8 and the x-coordinate of the first point is 0:
m = (0-2)/(0.8-0) = -2/0.8 = -2 ÷ 8/10 = -2 × 10/8 = -2/1 × 10/8 = -20/8 = -5/2