You will put x=0 and calculate the value of y=1 and then put y=0 and get value of x=1 and then put x=1 and get value of y=0 and then put y=1 and get x and so one , finally you could plot the graph.
Violet used 4 scoops of sugar and mixed it with 26 cups of lemonade and if it makes 234 cups of lemonade then there is 208. 26 scoops of sugar would violate the cups of lemonade.
