Answer:
Meg mix 
 of strawberry juice with each part of lemon juice
 of strawberry juice with each part of lemon juice
Explanation:
Given :Meg mixed 1 part of strawberry juice and 3 parts lemon juice to make lemonade 
To Find :How many parts of strawberry juice did Meg mix with each part of lemon juice?
Solution :
3 parts of lemon requires parts of strawberry juice = 1
1 part of lemon requires parts of strawberry juice = 

Hence Meg mix 
 of strawberry juice with each part of lemon juice
 of strawberry juice with each part of lemon juice