Answer:
Lydia was left with 9 peanut butter treats.
Explanation:
Let the chocolate chip cookies be = x
so the peanut butter treats will be = 144-x
Given ,the cookies and the treats are in a ratio of 5:3.
So,


This gives x=90
As Lydia has 90 chocolate chip cookies, so, the number of peanut butter treats = 144-x = 144-90 = 54
Now, Lydia's friend ate 2/5 of her cookies, it becomes =
Therefore, Lydia has 90-36=54 cookies left.
Now the total amount of baked goods remains = 144-54=90
Hence, remainder treats will be = 90-x
The new ratio is 6:1
So,


This gives x = 81
Hence, after eating 81 out 90 treats,Lydia is left with = 90-81 = 9 peanut butter treats.