Answer:
He will save $1.995 if he purchases it in the neighboring county
Explanation:
Don's county:
Sales tax of 7.75%.
So he pays
399 + 0.0775*399 = $429.9225
Neighboring county:
Sales tax of 7.25%.
So he pays
399 + 0.0725*399 = $427.9275
Savings:
429.9225 - 427.9275 = 1.995
He will save $1.995 if he purchases it in the neighboring county