The answer is 21 white socks.
WORK: there are a few approaches you can take to solve this one, but the one i used is converting 70% into a decimal so .7 Then i multiplied .7 x 30 and got the answer of 21. Another way to solve this is by finding 10% of 30 which is simple, it's 3! You can get this by doing 30/10. After you conclude that 3 is 10% of 30, you do 3 x 7 and get 21. You multiply by 7 here since 10% x 7 is 70% and that's what the question wanted.