Exercise 6.4.7: Write the following queries, based on the database schema Classes (class, type, country, numGuns, bore, displacement) Ships (name, class, launched) Battles (name, date) Outcomes (ship, battle, result) of Exercise 2.4.3, and evaluate your queries using the data of that exercise. a) Find the number of battleship classes. b) Find the average number of guns of battleship classes. ! c) Find the average number of guns of battleships. Note the difference be- tween (b) and (c); do we weight a class by the number of ships of that class or not? ! d) Find for each class the year in which the first ship of that class was launched