The correct option is A 840 cm2
Given:
The length of the rectangle, l=10 cm
The length of the rectangle, b=7 cm
Area of a rectangle (A) is the product of its length and breadth.
A=lb
A=10 cm×7 cm
A=70 cm2
Area of a rectangle formed by joining 12 of the rectangles is:
A′=12A
A′=12×70
A′=840 cm2