Margo has 40 milliliters of 25% soultion how many milliliters of 60% soultin should she add to obtain the required 30% solution

Using mixture formula:

Let volume be v, % be p

1 should be the first mixture, 2 should be the second mixture, 3 should be the final mixture.

p₁v₁ + p₂v₂ = p₃v₃

p₁ = 25%, v₁ = 40        p₂ = 60%, v₂ = ?    p₃ = 30%, v₃ =?

Let v₂ = x,  v₃ = total volumes = v₁ + v₂ = (40 + x)

Using:

p₁v₁ + p₂v₂ = p₃v₃

25*40 + 60*x = 30*(40 + x)

1000 + 60x = 1200 + 30x

60x - 30x = 1200 - 1000

30x = 200

x = 200/30

x = 20/3

Recall x = v₂, so she  has to add  20/3 milliters of the 60% solution in order to obtain 30% solution.

I hope this explains it.