Okay, here we have this:
Protein Supplement=75%--------->x pounds
Standard Protein= 25% ---------->(1500-x) pounds
Mixture 45% ----------------> 1500
75%x+25%(1500-x)=45%*1500
75x+25(1500-x)=67500
75x+37500-25x=67500
50x=30000
x=30000/50
x=600 pounds Protein Supplement
900 pounds standar Protein