You need a 45% alcohol solution. on hand, you have a 480 ml of a 40% alcohol mixture. you also have 85% alcohol mixture. how much of the 85% mixture will you need to add to obtain the desired solution?

x ml of 85% mixture will needed to add 

0.40*480 ml alcohol in 480 ml solution (40%)
0.85x alcohol in x ml solution (85%)

0.45(480 + x) in  (480 + x)ml 0.45% solution

 0.40*480+0.85x =0.45(480 + x) 
192+0.85x=216+0.45x
0.85x-0.45x=216-192
0.4x=24
x=24/0.4=60 ml  a 45% alcohol solution

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