Okay so this question is a system of equations.
Let's start by defining our variables.
Let x= 60 percent solution in mL and y= 80 percent solution
So the question tells us the solution will be 2000 mL
x+y=2000
Now the question also tells us that the he wants a solution with a 65 percent solution
(.60x+.80y)/(2000)=.65
Multiply by 2000, we get
.60x+.80y=1300
Then will take our first equation and solve for x
x=2000-y
Will then substitute it in for are x value in equation 2
.60(2000-y)+.80y=1300
simplify,
1200-.60y+.80y=1300
Add like terms
.20y=100
divide by .20
y=500
substitute for 500 for y in our first equation
x+y=2000
x+(500)=2000
x=1500
Then we have x=500 and y=1500, which means that we have 1500 mL of the 60 percent solution and 500 0f the 80 percent mL solution.