Can i get 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 the query or draw the query tree that will output the following:

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

Looks like a homework to me. What have you tried so far?. These are fairly straight forward queries requiring you to join tables or tuples in your case.