A submarine leaves its base on a heading of 100 degrees at a speed of 35 knots. It continues in that direction for 1.5 hours. It then changes its heading to 300 degrees and reduces its speed to 20 knots and continues at this speed for 2 hours. If the submarine top speed is 40 knots, what is the shortest amount of time that it will take to return to the base? In what direction must the sub travel?