a)

SELECT DISTINCT maker
FROM Product NATURAL JOIN PC
WHERE speed >= 1200;

b)

CREATE TEMPORARY TABLE temp SELECT MAX(price) AS maxPrinterPrice FROM Printer;

SELECT model
FROM Printer, temp
WHERE price = maxPrinterPrice;

c)

CREATE TEMPORARY TABLE temp SELECT MIN(speed) AS minPCSpeed FROM PC;

SELECT model
FROM Laptop, temp
WHERE speed < minPCSpeed;

d)

CREATE TEMPORARY TABLE temp SELECT model, price FROM PC;
INSERT INTO temp SELECT model, price FROM Laptop;
INSERT INTO temp SELECT model, price FROM Printer;

CREATE TEMPORARY TABLE temp2 SELECT MAX(price) AS maxPrice FROM temp;

SELECT model
FROM temp, temp2 
WHERE temp.price = temp2.maxPrice;

e)

CREATE TEMPORARY TABLE temp SELECT MIN(price) AS minColorPrinterPrice 
                            FROM Printer
                            WHERE color = "true";			    

CREATE TEMPORARY TABLE temp2 SELECT model
                             FROM Printer, temp
                             WHERE price = minColorPrinterPrice; 

SELECT DISTINCT maker
FROM Product NATURAL JOIN temp2;

f)

CREATE TEMPORARY TABLE minPCRam SELECT MIN(ram) AS ram FROM PC;

CREATE TEMPORARY TABLE maxSpeed SELECT MAX(speed) AS speed
                                FROM PC NATURAL JOIN minPCRam;

SELECT DISTINCT maker
FROM Product, maxSpeed, PC
WHERE maxSpeed.speed = PC.speed AND PC.model = Product.model;