Any help with relational Algebra? :(

I want to start learning about SQL, and wants to understand a little Relational Algebra.

I started with basic exercize, but dont know where to start.

I got 3 relations:

Ingredients(ingredients_id, iname, price)
Recipe(recipe_id, rname, type, portions)
Contains(recipe_id, ingredients_id, amount)

And now i want to write relational algebra that answers this 3:

1. a list with ingredients and amount for Recipe "Meatballs"
2. a list with all recipenames, for recipes that ONLY contains ingredients that costs less than 40
3. Recipename for recipes that contains "Eggs" but not "Chilli"

I hope u could help me, get started :(