I don't know where you went to school but wherever it was they didn't teach you much math. There is one and only one way to determine the percentage of unwed Black births. You create a fraction with the number of unwed Black births on the top and the total number of Black births on the bottom. Then you divide the top number by the bottom. You do the same thing for White mothers, dividing the number of illegitimate White births by the total number of White births. Then you can compare the percentage of illegitimate Black births to the percentage of illegitimate White births.
I don't know how old you are but you must be very young because there are countless studies and many millions of references to the number of unmarried births by race and they all show the same thing: About 70 percent of Black children are born to unwed mothers compared to about 30% for White mothers. You notion that the illegitimacy rate for Black mother is only about 10 is laughable. Here is one of millions of links:
“More than three quarters of African American births are to unmarried women, nearly double the illegitimacy rate of all other births, according to new federal data.
“The National Center for Health Statistics said that in 2015, 77.3 percent of non-immigrant black births were illegitimate. The national non-immigrant average is 42 percent, and it was 30 percent for whites.
“More than three quarters of African American births are to unmarried women, nearly double the illegitimacy rate of all other births, according to new federal data.
“The National Center for Health Statistics said that in 2015, 77.3 percent of non-immigrant black births were illegitimate. The national non-immigrant average is 42 percent, and it was 30 percent for whites."
77% black births to single moms, 49% for Hispanic immigrants
CONCLUSION: Every study, including those done by various government agencies and elements in the private sector prove the same thing: the percentage of illegitimate Black children is much higher than the percentage of illegitimate White children. I wouldn't be surprised if White mothers had a greater number (not percentage) of illegitimate births because there are a lot more White mothers (around six times as many).
PS: Using the figures you provided (415,000 Black babies born to unwed mothers and only a little over 500,000 total Black births), the percentage of illegitimate Black births would be 83 percent.