Subtract both sides from 6x, leaving you with the equation:
-2y=-6x+12
Now, you divide all of the sides by -2, therefore leabing you with the equation:
y=3x-6
4x-20+=-4
-4 -4
x-20=-8
+20 +20
x=12.
So, let's say the soft drink equals y and the sandwich equals x.
x + y = 9.9
The sandwich costs 3.5 times as much as the soft drink
x = 3.5y
Therefore, we can replace x with 3.5y since they're the same thing
3.5y + y = 9.9 <-- That's the equation :)
