Question 907018
We have 30 oz of 10% solution
We want to add some 0% solution  to make   4% solution
0*x+0.1*30=0.04(30+x)
0*x+3=1.2+0.04x
0x-0.04x=1.2-3
-0.04x=-1.8
x=45 oz of 0% (0) is added to 30 oz at 10%(3) to make 4% of 75 oz(3)
check
0*45+0.1*30=0.04(30+45)
0+3=0.04(75)
3=3
ok