I'm sure that you no longer need the answer, but I'll post this just in case someone else visits this post to find the answer.
The information you have is all you need to determine how much ethanol is needed. You just need to do some simple dimensional analysis.
0.3 g sulfanilamide X 1000mg/1g X 1 mL/210mg = 1.43 mL 95% ethanol
Therefore you will need 1.43 mL of 95% ethanol to dissolve 0.3g sulfanilamide.