Relational Algebra

I did the first and third question, but I am not sure if it is right. I do not know how to do the rest.

Write a relational algebra expression that returns the customer name that never bought any product of category electronic

Write a relational algebra expression that returns the store ID that sells electronics and these electronic items price is less than 100

Write a relational algebra expression that returns the average price of items bought by each customer

Question 1 (4 Points) Write a relational algebra expression that returns the name of the customer that bought product type 'apple TTcName (Oproduct type 'apple (customer)) Question 2 (5 Points) Write a relational algebra expression that returns total amount of money spent by Seain Question 3 (5 Points) Write a relational algebra expression that return the name of customer that bought all the product available at store 'tr08" TTcName(OSID-ro8(customer))