Final answer:
The cost of the plane ticket after tax is approximately $676.18.
Step-by-step explanation:
To find the total cost of the round-trip plane ticket after tax, we first need to calculate the amount of tax. Using the tax rate of 7.5%, we convert it to a decimal by dividing it by 100: 7.5/100 = 0.075. Next, we multiply this decimal by the cost of the plane ticket: 0.075 * $629 = $47.18. To find the cost after tax, we add the tax amount to the original cost: $629 + $47.18 = $676.18. Therefore, the cost of the plane ticket after tax is approximately $676.18.