The answer would be a 3x-4y=-10
90
Step-by-step explanation:vkjl
So to solve for y, we need to get y alone on one side of the equation. So we are going to subtract 9x from both sides of the equation to get:

And since y is negative, we are going to divide both sides by -1 in order to make the y positive:

If you graph it, it looks linear.
Answer:
The bill before the tip was $13.75 if you add a 20% tip of $2.75 the total bill including the tip would be $16.50
The bill before the tip is $13.75