Why were whites exempt from poll taxes and literacy tests?

Hello!

Whites were not obligated to pay poll taxes or take literacy tests. After African Americans were granted voting rights, many white men continued to try to restrict them from voting. 
Poll taxes were a form of voting restriction because many African Americans were very poor and could not afford to pay a tax to vote. This kept many African Americans away from the polls.
In addition, literacy tests were also used to restrict voting rights. White men explained that if a person is illiterate, he should not vote because he may not thoroughly understand what he is voting for. This lead to literacy tests, which were used to sway African Americans away from the polls because many were illiterate and/or uneducated. 
White men did not need to pay poll taxes or take literacy tests because many white men were well-educated and all were openly accepted at the polls. 

I hope this helps you! Feel free to comment or PM me with any additional questions that you may have. Have a great day!