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, for each manufacturer who sells PCs, the maximum price of a PC.
2. Find, for each speed of PC above 800, the average price.
3. Find the average hard-disk size of a PC for all those manufacturers that make printers.