-5x-16=8
-5x=24



above is how to correctly solve the equation
The error is in step 3.
Step 3 as written: 
This is incorrect because you are removing the 5 from the -5x so it wouldn't be in the numerator.
Hope this helps
Answer:
See below
Step-by-step explanation:
You just need 1/4 of everything:
1/4 c peanut butter
1/4 c brown sugar
1/4 c gran sugar
1/4 c butter
1/2 egg
1/4 tsp baking soda
1/4 tsp baking powder
1/4 tsp vanilla
5/8 c flour