An amphitheatre has 15 seats in the first row, 19 in the second, 23 in the third, and so on, for 34 rows. How many seats are in the amphitheatre?

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.