A dehydrated patient needs a 3.82% saline IV. Unfortunately, the hospital only has bags of 4% and 3% saline solutions. How many liters of each of these solutions should be mixed together to yield 5 liters of the desired concentration?

Question

So far I've come up with this:

x= 4% solution; y= 3% solution
x + y = 5
4x + 3(5-x) = 3.82
4x + 15 -3x = 3.82 subtracting 15 from both sides
1x = -11.18
x= -11.18