The city of Springfield has a sales tax of $7\mathrm{.}5\%.$ This tax would be considered $\_\_\_\_\_\_.$

a$.$

proportional because the percentage of the tax is the same for everyone

b$.$

proportional because you can deduct sales taxes paid from federal income tax and get a rebate if you have paid more than a maximum percent of your income in taxes

c$.$

progressive because people with higher incomes tend to spend a greater share of their income on goods subject to sales taxes

d$.$

regressive because people with lower incomes tend to spend a greater share of their income on goods subject to sales taxes