How many 4' x 8' sheets of plywood are required to cover a floor that is 9 m by 16 m?

Assuming no border or waste, 9m by 16 m translates to 29.52' x 52.49'.
use 32/8=4 sheets of plywood to cover the width on the 8' side.
For the length, use 52/4=13 pieces on the 4' side.  
This gives a total of 4*13=52 sheets.
The extra 0.49' x 29.52 can be covered using the extra from the last four sheets for the width.

Check: 
Area to be covered: 29.52*52.49=1550 sq. ft.
Area of plywood supplied = 52*4'x8'= 1664 sq. ft, > 1550 sq.ft.