A diver begins at sea level and descends into a cave at 3.1/2 feet per second. He descends for 30 seconds. Then he swims back up to the surface in 21 seconds. What was his speed going back up to the surface?

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.