Joe earns $$20,000$ a year. He pays an average tax rate of $10$ percent.

Kelly earns $$40,000$ a year. She pays an average tax rate of $7\mathrm{.}5$ percent.

What type of income tax do Joe and Kelly face?

Joe and Kelly face a income tax.

A$.$ flat$-$rate

B$.$ regressive

C$.$ proportional

D$.$ progressive