Ok... we'll do the same here, elimination
g = carbs in one glass of milk
b = carbs in a snack bar
in this, we can simply multiply by -2 at the bottom to get a -4g, and thus "eliminate" the g-variable
g = carbs in one glass of milk
b = carbs in a snack bar
in this, we can simply multiply by -2 at the bottom to get a -4g, and thus "eliminate" the g-variable