What is the significant concentration of 75.0 of ethanol dissolve in 580.0 g of water?
Frankly I don't know what "significant concentration" is. My assumption is that you want percent by weight (by mass).
% w/w = [75.0/(580 + 75.0)]*100 = ?
% w/w = [75.0/(580 + 75.0)]*100 = ?