Answer:
A
Step-by-step explanation:
Let x ml be the amount of paint color B mixed with 40 ml of paint color A.
In 40 ml of paint color A are 15% of black pigment, so there are
[tex]0.15\cdot 40\ ml[/tex]
of black pigment.
In x ml of paint color B are 60% of black pigment, so there are
[tex]0.6\cdot x\ ml[/tex]
of black pigment.
In total we het x+40 ml of mixture. There are 25% of black pigment that is
[tex]0.25\cdot (x+40)\ ml.[/tex]
Thus,
[tex]0.15\cdot 40+0.6\cdot x=0.25\cdot (x+40).[/tex]
