Consider the following database schema:

Product(maker, model, type)

PC(model, speed, ram, hd, rd, price)

Laptop(model, speed, ram, hd, screen, price)

Printer(model, color, type, price)

1. (Grouping and Aggregation) Write the following queries in SQL:

1. Find the average speed of laptops costing over $2000.
2. Find the average price of PCs and laptops made by manufacturer D.
3. Find, for each manufacturer, the average screen size of its laptops.
4. Find the manufacturers that make at least three different models of PC.
5. Find, for each manufacturer who sells PCs, the maximum price of a PC.
6. Find, for each speed of PC above 800, the average price.
7. Find the average hard-disk size of a PC for all those manufacturers that make printers.