1.5 liters
Let's make an equation to represent the cost of the resulting solvent.
80*A + 25*B = 36(A+B)
Where
A = amount of $80 per liter solvent
B = amount of $25 per liter solvent
So let's plug in the value 6 for B, then solve for A.
80*A + 25*B = 36(A+B)
80*A + 25*6 = 36(A+6)
80*A + 150 = 36(A+6)
80*A + 150 = 36A + 216
44*A + 150 = 216
44*A = 66
A = 66/44 = 1.5
So you need 1.5 liters of the $80 per liter solvent.
