Database Relational Algebra problems

Consider two relation instances below, with the following schemas: Country (country name, continent); City (city name, country name. is_capital, population). In each question (a)-(d) below, write a relational algebra expression and show its result when the expression is executed with the given instances. List the names of all European cities with population of more than 600,000. List the names of all countries for which no cities have been entered into the City table. List names and continents of countries that are either in Europe or whose capitals have a population of over 1 million. List all pairs of cities such that one of them is a capital of some country, and the other is a non-capital city in that same country. For each city in the pair, list its name