Well.. instead of k he could have put 7. He should know that x and y are cut in half of their original values.
Hope I helped you!
X-ounces of an oil blend,
y - ounces of glycerin
x + y = 4 ⇒ y = 4 - x
1.5 x + y = 5.50
1.5 x + 4 - x = 5.50
0.5 x = 5.50 - 4
0.5 x = 1.50
x = 3
y = 4 - 3 = 1
There are 3 ounces of an oil blend and 1 ounce of glycerin.
