1' = 0.3048 m.
4' by 8' = 4*0.3048 m by 8*.3048 m = 1.2192 m by 2.4384 m
The area of a sheet of plywood is (1.2192 m)·(2.4384 m) = 2.97289728 m².
The area of the floor is (9 m)·(16 m) = 144 m².
Dividing floor area by sheet area gives us the number of sheets required.
... (144 m²)/(2.97289728 m²) ≈ 48.44 . . . . sheets
That is, 49 sheets of plywood are required.
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Due to the mismatch of dimensions, considerable cutting and fitting will be required.