Answer:
One cup of lemonade will cost $2.
Explanation:
From simple observation and visual inspection we can conclude that one cup of lemonade costs $2.
If 9 cups of lemonade cost $18 then one cup of lemonade will cost $18÷9 = $2
If 2 cups of lemonade cost $4 then one cup of lemonade will cost $4÷2 = $2.
Therefore we can conclude that one cup of lemonade will cost $2.