Since 40% of the liquid is water, then .4x = 1L
Then you solve for x.
0.4x=1L
0.4x/0.4 = 1L/0.4
x = 2.5 L
So we have the total volume of the bottle which is 2.5 L.
Now, let the number of liters of lemon juice be y.
y=0.6x
So the equation would be x = 0.4x + y
or simply, x = .4x + .6x
Solve for y.
y= 0.6(2.5L)
y= 1.5L
So the amount of lemon juice in the bottle is 1.5 L.