Step-by-step explanation:
If x is the volume of 50% solution and y is the volume of 80% solution, then the total volume is:
x + y = 180
And the total amount of antifreeze is:
0.50(x) + 0.80(y) = 0.75(180)
0.5x + 0.8y = 135
Solving the system of equations:
0.5x + 0.8(180 − x) = 135
0.5x + 144 − 0.8x = 135
9 = 0.3x
x = 30
y = 180 - x
y = 150
You need 30 gallons of 50% solution and 150 gallons of 80% solution.