You need a 65% alcohol solution. On hand, you have a 450 mL of a 40% alcohol mixture. You also have 95% alcohol
mixture. How much of the 95% mixture will you need to
add to obtain the desired solution?

375 ml of 95%  is what we need to obtain the desired solution

Explanation:

Solution

Now

450 ml of 40% alcohol mixture +95% mix of x = 65% (450 +x)

Thus

0.40 * 450 +0.95 x = 0.65 (450 + x)

180 + 0.95 x =0.65 (450 +x)

180 +0.95 x = 292.5 + 0.65 x

So,

0.95 x - 0.65 x = 292.5 - 180

= 0.3 x = 112.5

x =112.5/0.3

x= 375 ml

Therefore, we will need 375 ml of 95% solution