Let x be the number of liters of the 40% antifreeze solution to be used, and y be the number of liters of the 70% antifreeze solution to be used.
We can start by setting up two equations based on the information given:
Equation 1: x + y = 240 (total volume of the mixture is 240 liters)
Equation 2: 0.4x + 0.7y = 0.64(240) (total amount of antifreeze in the mixture is 64% of 240 liters)
Simplifying Equation 2, we get:
0.4x + 0.7y = 153.6
Now we can use Equation 1 to solve for one of the variables in terms of the other. Let's solve for y:
y = 240 - x
Substituting this into Equation 2, we get:
0.4x + 0.7(240 - x) = 153.6
Simplifying and solving for x, we get:
0.4x + 168 - 0.7x = 153.6
-0.3x = -14.4
x = 48
So we need 48 liters of the 40% antifreeze solution. Using Equation 1 to find y, we get:
y = 240 - x = 240 - 48 = 192
So we need 192 liters of the 70% antifreeze solution.
Therefore, 48 liters of the 40% antifreeze solution and 192 liters of the 70% antifreeze solution should be mixed to obtain 240 liters of a 64% antifreeze solution.