Weird. I think you just need to look if the point falls on the shaded area. But only (-5,5) does ...
Find out how much you need for one person then multiply by 18 is one way you could do this..
4 divided by 24 = 0.166666666666667 x 18 = 3 litres of lemon-lime soda.
2 divided by 24 = 0.083333333333333 x 18 = 1.5 pints of servet
6 divided by 24 = 0.25 x 18 = 4.5 cups of ice.
Hope this helps!
Your teacher may have wanted you to (some how) use your 6x tables to work this out?!
This will generate a line quickly dropping from left to right, with an x-intercept of 0.4 and a y-intercept of 2.
See the attached image for the actual graph.
I hope you find my answer helpful I got 39,000.