Question 127483
5b+3.5(30-b)=4*30
5b+105-3.5b=120
1.5b=120-105
1.5b=15
b=15/1.5
b=10 pounds of Brazil nuts is needed.
30-10=20 pounds of Walnuts is needed. 
Proof:
5*10+3.5(30-10)=4*30
50+3.5*20=120
50+70=120
120=120