As can be seen from the diagram, the length of the side of the square floor is the sum of the lengths of the side of square A and square B.
The side of the A type square is 1600 $(cm^2)$ and
$1600 = 40.40$
Then the magnitude of the side of square A is 40 (cm).
The side of the B type square is 900 $(cm^2)$ and
$900 = 30.30$
Then the magnitude of the side of square A is 30 (cm).
The length of the side of the square floor is
$30 + 40 = 70$ (cm)
The area of the square floor is
$70 \times 70 = 4900$ ($cm^2$)
Moreover, can be seen from the diagram that the area of the square floor equal to the total area of 3 B type squares, 1 A type square and the area of the shaded part.
Then, the area of the shaded part ís
$4900 - 1600 - 900 \times 3 = 600$ ($cm^2$)
Then the quare tiles of area $100cm^2$ required to pave the shaded part is
$600 : 100 = 6$ (tiles)
The answer is A.
