1. **State the problem:** A watch costs 86 before tax and 87.72 after tax. We need to find the sales tax percentage. 2. **Formula used:** The total price after tax is given by: $$\text{Total Price} = \text{Original Price} + \text{Tax Amount}$$ Or equivalently: $$\text{Total Price} = \text{Original Price} \times (1 + \text{Tax Rate})$$ where Tax Rate is in decimal form. 3. **Set up the equation:** Let the sales tax rate be $r$ (in decimal). Then: $$87.72 = 86 \times (1 + r)$$ 4. **Solve for $r$:** $$1 + r = \frac{87.72}{86}$$ $$1 + r = 1.02$$ 5. **Isolate $r$:** $$r = 1.02 - 1$$ $$r = 0.02$$ 6. **Convert to percentage:** $$r \times 100 = 0.02 \times 100 = 2\%$$ **Final answer:** The sales tax percentage is **2%**.