By 1860 what percentage of white southerners owned between 10-99 slaves

6.6%

Explanation: According to The Gilder Lehrman Institute of American History's research on statistics of slaves and slaveholdings, about 6.6% of the white southerners in 1860 owned between 10 and 99 slaves.

The 76.1% of the population did not own slaves, the 17.2% owned less than 10 slaves and a 0.1% owned more than 100 slaves.

i beleive a. is the only possible answer