Answer: The cost of appetizer is $8 and the cost of dessert is $6.
Explanation:
Let cost of appetizer be 'x'.
Let cost of desserts be 'y'.
According to question,
On Tuesday, it becomes,

On Friday, it becomes,

By graphing method, we get that,
x= 8 and y = 6
Hence, the cost of appetizer is $8 and the cost of dessert is $6.